Physical Graffiti

Physical Graffiti is the sixth studio album by the English rock band Led Zeppelin. It was released as a double album on 24 February 1975. It was the group's first album to be released under their new label, Swan Song Records.

The band wrote and recorded eight new songs for the album in early 1974 at Headley Grange, a country house in Hampshire, which gave them ample time to improvise arrangements and experiment with recording. The total playing time covered just under three sides of an LP, so they decided to expand it into a double by including previously unreleased tracks from the sessions for the earlier albums Led Zeppelin III, Led Zeppelin IV and Houses of the Holy. The album covered a range of styles including hard rock, progressive rock, rock 'n' roll and folk. The album was then mixed over summer 1974 and planned for an end-of-year release; however, its release was delayed because the Peter Corriston-designed die-cut album cover proved difficult to manufacture.

Physical Graffiti was commercially and critically successful upon its release and debuted at number one on album charts in the UK and number three in the US. It was promoted by a successful US tour and a five-night residency at Earl's Court, London. The album has been reissued on CD several times, including an expansive 40th anniversary edition in 2015. Physical Graffiti was later certified 16× platinum in the United States by the Recording Industry Association of America (RIAA) in 2006, signifying shipments of over eight million copies.

## Recording

The first attempt by Led Zeppelin to record songs for Physical Graffiti took place in November 1973 at Headley Grange in Hampshire, England, where they had previously recorded their untitled fourth album. The recording equipment consisted of Ronnie Lane's Mobile Studio. Guitarist and producer Jimmy Page and drummer John Bonham recorded an instrumental which was later reworked as "Kashmir" during this visit. However, these sessions came to a halt quickly and the studio time was turned over to Bad Company, who used it to record songs for their debut album. The press reported that bassist/keyboardist John Paul Jones was ill and unable to record. However, he became disillusioned with the group and fed up with touring, and told manager Peter Grant he was considering quitting. Grant asked him to reconsider and take the rest of the year off to recuperate.

The group reconvened at Headley Grange in January and February 1974, where they recorded eight tracks engineered by Ron Nevison. Lead singer Robert Plant later referred to these eight tracks as "the belters", including "off-the-wall stuff that turned out really nice". As with previous sessions at Headley Grange, the informal atmosphere allowed the group to improvise and develop material while recording. Sometimes the group would rehearse or record a track several times, discuss what went wrong or what could be improved and then realised they had worked out an alternative arrangement for it which was better. Bonham was a driving force at the sessions, regularly suggesting ideas or the best ways in which a complicated arrangement could be played successfully. This led to him getting a lead songwriting credit on several tracks.

The eight songs extended beyond the length of a conventional album, almost spanning three sides of an LP, so the group decided to create a double album, adding material they had recorded for previous albums but never issued. This included various jam sessions such as "Boogie With Stu", which Page thought would be unsuitable as a track on a single album. Additional overdubs were laid down, and the final mixing of the album was performed in July 1974 by Keith Harwood at Olympic Studios, London. The title "Physical Graffiti" was coined by Page to illustrate the whole physical and written energy that had gone into producing the set.

## Songs

The album spanned several years of recording and covered a range of musical styles, including hard rock ("Custard Pie", "The Rover", "The Wanton Song", "Sick Again", "Houses of the Holy"), eastern-influenced orchestral rock ("Kashmir"), progressive rock ("In the Light"), driving funk ("Trampled Under Foot"), acoustic rock and roll ("Boogie with Stu", "Black Country Woman"), love ballad ("Ten Years Gone"), blues rock ("In My Time of Dying"), soft rock ("Down by the Seaside"), country rock romp ("Night Flight"), and acoustic guitar instrumental ("Bron-Yr-Aur").

Several tracks from the album became live staples at Led Zeppelin concerts. In particular, "In My Time of Dying", "Trampled Under Foot", "Kashmir", "Ten Years Gone", "Black Country Woman", and "Sick Again" became regular components of the band's live concert set lists following the release of the album.

### Side one

"Custard Pie" was recorded at Headley Grange in early 1974. The first take was played at a faster tempo than the finished version, with various improvised vocals. After a basic run-through, the group then discussed possibilities for rearranging it. Page played the guitar solo through an ARP synthesiser, while Jones overdubbed a Hohner Clavinet part and Plant played harmonica.

"The Rover" was written in 1970 at Bron-Yr-Aur, a cottage near Machynlleth, Wales. It was first recorded at Headley Grange in May 1970 as an acoustic number for Led Zeppelin III. It was reworked as an electric number in 1972 for Houses of the Holy, which formed the basis for the backing track. Page subsequently added guitar overdubs in 1974 with Keith Harwood engineering.

"In My Time of Dying" is based on a traditional song that Bob Dylan recorded on his debut album in 1962. The track was recorded live, with Page later adding further slide guitar overdubs. The arranging and structuring was led by Bonham, who worked out where the various stop / start sections in the track should be, and how the group would know where to come back in. The very end of the song features his off-mic cough, causing the rest of the group to break down at that point. Bonham subsequently shouted "That's got to be the one, hasn't it?", feeling it was the best take. It was left on the album to show fans that Led Zeppelin were a working band that took care in their recordings.

### Side two

"Houses of the Holy" was recorded as the title track for the album of the same name in May 1972 at Olympic Studios with Eddie Kramer engineering. It was left off that album because of its similarity to other tracks such as "Dancing Days", which were felt to be better. Unlike some of the other older material on Physical Graffiti, it required no further overdubbing or remixing.

"Trampled Under Foot" developed from a jam session driven by Jones at the Clavinet. The song went through several arrangement changes before arriving at the version heard on the album, with the group rehearsing various different ideas and arguing about the overall style. Bonham decided the track was too "souly" and rearranged it into a funk style, suggesting that Page should play a guitar riff throughout in place of chords. The lyrics are a series of double entendres around driving and cars. The song quickly became a popular live piece that was played at every live show from 1975 onwards, and was later revived by Plant for his solo tours. It was released as a single in the US on 2 April (with "Black Country Woman" as the B-side) and was a top 40 hit.

"Kashmir" was an idea from Page and Bonham, and was first attempted as an instrumental demo in late 1973. Plant wrote the lyrics while on holiday in Morocco. Jones played Mellotron on the track, and arranged strings and brass parts that were played by session musicians. The song was one of the most critically acclaimed on the album, and was played at every gig from 1975 onwards. Page and Plant played it on their 1994 tour, and it was reworked in 1998 by Sean "Puffy" Combs for his single "Come With Me" which featured Page on guitar.

### Side three

"In the Light" was recorded at Headley Grange in early 1974. It was initially called "In the Morning" and went through several rehearsals and takes to work out a basic structure. A drone / chant introduction was later added to the piece.

"Bron-Yr-Aur" was a solo acoustic piece by Page, named after the cottage where he had composed and arranged much of Led Zeppelin III with Plant. It was recorded at Island Studios in mid-1970. The track was later used as background music in the group's film The Song Remains the Same.

"Down by the Seaside" was originally written as an acoustic track at Bron-Yr-Aur in 1970, and was influenced by Neil Young. It was reworked as an electric track during sessions for the fourth album the following year. Page and Bonham led the arranging, changing tempo from the slow to fast section and then back again.

"Ten Years Gone" was mostly composed by Plant about an old love affair, and was combined with an instrumental piece from Page, featuring overdubbed electric and acoustic guitar parts. When the track was performed live, Jones played a triple-neck guitar featuring mandolin, six- and twelve-string guitars, in order to try to reproduce the various guitar overdubs on the studio recording.

### Side four

"Night Flight" was recorded at Headley Grange in 1971 for the fourth album. Besides the usual bass, Jones plays Hammond organ on the track, and Page plays guitar through a Leslie speaker. Plant wrote the lyrics after reading a news headline entitled "Nuclear Damage Test Threat" and wondered why there seemed to be little peace and love in the world.

"The Wanton Song" was built around a Page guitar riff. Unlike some of the other tracks recorded at the 1974 Headley Grange sessions, it was straightforward to arrange, with the group building the song around the riffs.

"Boogie with Stu" was a jam session with Rolling Stones pianist Ian Stewart based around the Ritchie Valens song "Ooh My Head". It was recorded in 1971 at Headley Grange during the same session that produced "Rock and Roll" for the fourth album. It did not credit Valens or Bob Keane, instead crediting Valens' mother. Eventually, a lawsuit was filed by Keane, and half of the award went to Valens' mother, although she was not part of the suit.

"Black Country Woman" was recorded in the garden at Stargroves in 1972 for Houses of the Holy, as part of the group's desire to work in "off the wall" locations outside a traditional studio environment. The track was nearly abandoned when an aeroplane cruised overhead, but it was left on the final recording for effect.

"Sick Again" was written by Page and Plant about the 1973 tour and their experience with meeting groupies. The track was driven by Bonham's drumming and Page's guitar riffs. The arrangement had been worked out before recording, and was straightforward to put down on tape.

### Unreleased material

As Physical Graffiti collected various out-takes from earlier albums, little was left over from the recording sessions that was not eventually released. An early arrangement of "Custard Pie", different from the final version, was reworked as "Hots on For Nowhere" on the following album, Presence. A number of other outtakes from earlier album sessions that had not been put on Physical Graffiti were later included on the 1982 album Coda.

## Artwork and packaging

The album was originally released with a die-cut sleeve design depicting a New York City tenement block, through whose windows various cultural icons could be interchangeably viewed. The album designer, Peter Corriston, was looking for a building that was symmetrical with interesting details, that was not obstructed by other objects and would fit the square album cover. He subsequently came up with the rest of the cover based on people moving in and out of the tenement, with various sleeves that could be placed under the main cover and filling the windows with various pieces of information. Incidentally, the same front doorway and stoop at 96 St. Mark's Place is also the location used by The Rolling Stones for their music video promoting their single "Waiting on a Friend" from their 1981 album Tattoo You.

The two five-storey buildings photographed for the album cover are located at 96 and 98 St. Mark's Place in New York City. The original photograph underwent a number of tweaks to arrive at the final image. The fourth floor of the building had to be cropped out to fit the square album cover format.

Eschewing the usual gatefold design in favour of a special die-cut cover, the original album jacket included four covers made up of two inners (for each disc), a middle insert cover and an outer cover. The middle insert cover is white and details all the album track listings and recording information. The outer cover has die-cut windows on the building, so when the middle cover is wrapped around the inner covers and slid into the outer cover, the title of the album is shown on the front cover, spelling out the name "Physical Graffiti". Images in the windows touched upon a set of American icons and a range of Hollywood ephemera. Pictures of W. C. Fields and Buzz Aldrin alternated with the snapshots of Led Zeppelin. Photographs of Lee Harvey Oswald, Marcel Duchamp and Pope Leo XIII are also featured. Per the liner notes, package concept and design was by AGI/Mike Doud (London) and Peter Corriston (New York). Photography was by Elliott Erwitt, B. P. Fallon, and Roy Harper. "Tinting Extraordinaire": Maurice Tate, and window illustration by Dave Heffernan. In 1976 the album was nominated for a Grammy Award in the category of best album package.

## Release and critical reception

Physical Graffiti was Led Zeppelin's first release on their own Swan Song Records label, which had been launched in May 1974. Until this point, all of Led Zeppelin's albums had been released on Atlantic Records, who would distribute Swan Song. The album was first announced to the press on 6 November with a planned release date of 29 November and an accompanying US tour (the band's tenth) starting in January. Delays in the production of the album's sleeve design prevented its release prior to the commencement of the tour. It was finally released on 24 February 1975.

The album was a commercial and critical success, having built up a huge advance order following the delayed release date, and when eventually issued it reached No. 1 in the UK charts. In the US, it debuted at No. 3 on the Billboard Pop Albums chart, rising to No. 1 the following week and staying there for six weeks. Physical Graffiti has since proven to be one of the most popular releases by the group, shipping 8 million copies in the United States. It was the first album to go platinum on advance orders alone. Shortly after its release, all previous Led Zeppelin albums simultaneously re-entered the top-200 album chart.

The group debuted several songs from Physical Graffiti live for the first time at a warm-up gig in Rotterdam, Netherlands on 11 January, a week before the US tour, which lasted until 27 March. The tour was also successful, and was followed up by a series of shows at Earl's Court, London. Tickets for the shows sold out within four hours, described by promoter Mel Bush as "unprecedented demand in the history of rock music", so a further two dates were added. The shows attracted rave reviews, and critics noted the band enjoyed playing the new material on Physical Graffiti more than the older songs.

NME's Nick Kent reviewed the album three months before it was released. He speculated it could be the group's best work to date, saying "the album's tonal density is absolutely the toughest, most downright brutal I've heard all year". In March 1975, Billboard magazine's reviewer wrote: "[Physical Graffiti] is a tour de force through a number of musical styles, from straight rock to blues to folky acoustic to orchestral sounds." Similarly, Jim Miller stated in Rolling Stone that the double album was "the band's Tommy, Beggar's Banquet and Sgt. Pepper rolled into one: Physical Graffiti is Led Zeppelin's bid for artistic respectability". Village Voice critic Robert Christgau maintained his long-held ambivalence regarding Led Zeppelin, writing that except for side two, the material often wanders into "wide tracks, misconceived opi, and so forth", and "after a while Robert Plant begins to grate".

In 2003, Rolling Stone ranked it at number 70 on the magazine's list of the "500 Greatest Albums of All Time." It was re-ranked at number 73 in a 2012 revised list, and re-ranked at number 144 in 2020.

Plant later felt that Physical Graffiti represented the band at its creative peak, and has since said that it is his favourite Led Zeppelin album. Page has also said the album was a "high-water mark" for the group, and the creative energy from jamming and gradually working out song structures together led to some strong material. Reviewing the album for BBC Music in 2007, Chris Jones described it as "a towering monument to the glory of Zeppelin in their high-flying heyday".

(\*) designates unordered lists.

## Reissues

Physical Graffiti was first issued on CD as a double-disc set in 1987. However, it was done without input from the band, and the first pressing accidentally edited off the studio banter at the end of "In My Time of Dying" (later fixed on repressings). Page was unhappy with his lack of input over the CDs and decided he would produce new versions himself. He booked a week in May 1990 with engineer George Marino to remaster the entire back catalogue. Eight tracks from Physical Graffiti appeared on the four-disc Boxed Set and three on Remasters, both in 1990; the remainder appeared on Boxed Set 2 in 1993, while the album was properly reissued in 1994.

An extended remastered version of Physical Graffiti was reissued on 23 February 2015, almost exactly forty years after the original album was released. The reissue comes in six formats: a standard two-CD edition, a deluxe three-CD edition, a standard two-LP version, a deluxe three-LP version, a super deluxe three-CD plus three-LP version with a hardback book, and as high resolution 24-bit/96k digital downloads. The deluxe and super deluxe editions feature bonus material containing alternative takes and arrangements of songs. The reissue was released with an altered colour version of the original album's artwork as its bonus disc's cover.

## Track listing

### Original release

### Deluxe edition (2015)

## Personnel

Led Zeppelin

- Robert Plant – vocals, harmonica
- Jimmy Page – electric, acoustic, lap steel and slide guitars, production
- John Paul Jones – bass guitar, mandolin, acoustic guitar, keyboards, Mellotron
- John Bonham – drums, percussion

Additional musicians

- Ian Stewart – piano on "Boogie with Stu"
- Uncredited session musicians – strings and horns on "Kashmir"

Production

- George Chkiantz – engineering at Olympic (1972)
- Keith Harwood – engineering at Olympic (1974)
- Andy Johns – engineering at Island (1970 & 1971) and Headley Grange (1971)
- Eddie Kramer – engineering at Stargroves (1972)
- Ron Nevison – engineering at Headley Grange (1974)
- Peter Grant – executive producer
- George Marino and Jimmy Page – remastered CD release

Artwork

- Peter Corriston – artwork, design, cover design
- Mike Doud – artwork, design, cover design
- Elliot Erwitt – photography
- B. P. Fallon – photography
- Roy Harper – photography
- Dave Heffernan – illustrations

## Charts

### Weekly charts

### Year-end charts

## Certifications

## See also

- List of best-selling albums in the United States

Albums recorded at Electric Lady Studios

Albums recorded at Olympic Sound Studios

Albums with cover art by Peter Corriston


King Island emu

The King Island emu (Dromaius novaehollandiae minor) is an extinct subspecies of emu that was endemic to King Island, in the Bass Strait between mainland Australia and Tasmania. Its closest relative may be the extinct Tasmanian emu (D. n. diemenensis), as they belonged to a single population until less than 14,000 years ago when Tasmania and King Island were still connected. The small size of the King Island emu may be an example of insular dwarfism. The King Island emu was the smallest of all known emus and had darker plumage than the mainland emu. It was black and brown and had naked blue skin on the neck, and its chicks were striped like those on the mainland. The subspecies was distinct from the likewise small and extinct Kangaroo Island emu (D. n. baudinianus) in a number of osteological details, including size. The behaviour of the King Island emu probably did not differ much from that of the mainland emu. The birds gathered in flocks to forage and during breeding time. They fed on berries, grass and seaweed. They ran swiftly and could defend themselves by kicking. The nest was shallow and consisted of dead leaves and moss. Seven to nine eggs were laid, which were incubated by both parents.

Europeans discovered the King Island emu in 1802 during early expeditions to the island, and most of what is known about the bird in life comes from an interview French naturalist François Péron conducted with a sealer there, as well as depictions by artist Charles Alexandre Lesueur. They had arrived on King Island in 1802 with Nicolas Baudin's expedition, and in 1804 several live and stuffed King and Kangaroo Island emus were sent to France. The two live King Island specimens were kept in the Jardin des Plantes, and the remains of these and the other birds are scattered throughout various museums in Europe today. The logbooks of the expedition did not specify from which island each captured bird originated, or even that they were taxonomically distinct, so their status remained unclear until more than a century later. Hunting pressure and fires started by early settlers on King Island likely drove the wild population to extinction by 1805. The captive specimens in Paris both died in 1822 and are believed to have been the last of their kind.

## Taxonomy

There was long confusion regarding the taxonomic status and geographic origin of the small island emu taxa from King Island and Kangaroo Island, since specimens of both populations were transported to France as part of the same French expedition to Australia in the early 1800s. The logbooks of the expedition failed to clearly state where and when the small emu individuals were collected, and this has resulted in a plethora of scientific names subsequently being coined for either bird, many on questionable grounds, and the idea that all specimens had originated from Kangaroo Island. Furthermore, in 1914, L. Brasil argued the expedition did not encounter emus on King Island, because the weather had been too bad for them to leave their camp. The French also referred to both emus and cassowaries as "casoars" at the time, which has led to further confusion.

The French naturalist Louis Jean Pierre Vieillot coined the binomial Dromaius ater in 1817. Various collectors found subfossil emu remains on King Island during the early 20th century, the first by the Australian amateur ornithologist Archibald James Campbell in 1903, near a lagoon on the east coast. In 1906, the Australian ornithologist Walter Baldwin Spencer coined the name Dromaius minor based on some Pleistocene subfossil bones and eggshells found on King Island, which he considered distinct from D. ater (then thought to be from Kangaroo Island) due to the smaller size of the former. The Australian ornithologist William Vincent Legge also coined a name for these remains in 1906, Dromaius bassi, but at a later date. In his 1907 book Extinct Birds, the British zoologist Walter Rothschild stated that Vieillot's description actually referred to the mainland emu, and that the name D. ater was therefore invalid. Believing the skin in Muséum national d'Histoire naturelle of Paris was from Kangaroo Island, he made it the type specimen of his new species Dromaius peroni, named after the French naturalist François Péron, who is the main source of information about the bird in life. Spencer reported more emu bones from King Island in 1910, which he compared to bones from Kangaroo Island which were by then considered to belong to D. peroni. The Australian amateur ornithologist Gregory Mathews coined further names in the early 1910s, including a new genus name, Peronista, as he believed the King and Kangaroo Island birds were generically distinct from the mainland emu.

Later writers claimed that the subfossil remains found on King and Kangaroo Islands were not discernibly different, and that they therefore belonged to the same taxon. In 1959, the French ornithologist Christian Jouanin proposed that none of the skins were actually from Kangaroo Island, after inspecting expedition and museum documents. In 1990, Jouanin and the French palaeontologist Jean-Christophe Balouet used environmental forensics to demonstrate that the mounted skin in Paris came from King Island, and that at least one live bird had been brought from each island. All scientific names given to the Kangaroo Island emu were therefore based on specimens from King Island or were otherwise invalid, leaving it nameless. Based on later finds of subfossil material in 1984, the Australian ornithologist Shane A. Parker confirmed the separate geographic origin and distinct morphology of the King and Kangaroo Island emus, finding that the latter was larger. Parker named the Kangaroo Island bird Dromaius baudinianus, after Nicolas Baudin, the leader of the French expedition. The name Dromaius ater was kept for the King Island emu.

There are few morphological differences that distinguish the extinct insular emus from the mainland emu besides their size, but all three taxa were most often considered distinct species. A 2011 study by the Australian geneticist Tim H. Heupink and colleagues of nuclear and mitochondrial DNA, which was extracted from five subfossil King Island emu bones, showed that its genetic variation fell within that of the extant mainland emus. It was therefore interpreted as conspecific with the emus of the Australian mainland, and was reclassified as a subspecies of Dromaius novaehollandiae, D. n. ater. Other animals present on King Island are also considered as subspecies of their mainland or Tasmanian counterparts rather than distinct species. The authors suggested that further studies using different methods might be able to find features that distinguish the taxa. In its 2013 edition, The Howard and Moore Complete Checklist of the Birds of the World emended the trinomial name of the King Island emu to D. n. minor, based on Spencer's D. minor, on the ground that Vieillot's D. ater was originally meant for the mainland emu. This rationale was accepted by the IOC World Bird List, which used D. n. minor thereafter.

In 2014–2015, the English palaeontologist Julian Hume and colleagues conducted a search for emu fossils on King Island; no major palaeontological surveys had been done since the early 20th century, apart from discoveries made by the local natural historian Christian Robertson during the preceding thirty years. In 2014, Hume and colleagues found emu subfossils in Cape Wickham, but upon returning to the site in 2015, the area had been turned into a golf course, and the researchers were denied access to the site. They cautioned in 2018 that other fossiliferous sites on King Island were also under such threat, and highlighted the need to protect them. The researchers also identified an area near Surprise Bay where subfossils had been collected in 1906, but found it almost impossible to find more, since the area had been covered in grass in the meantime (the grass had previously been kept down by livestock). In 2021, Hume and Robertson reported a King Island emu eggshell missing a few pieces, which Robertson had discovered in a sand dune during fieldwork. This the only known almost complete egg of this emu, glued together from broken pieces.

### Evolution

During the Late Quaternary period (0.7 million years ago), small emus lived on a number of offshore islands of mainland Australia. In addition to the King Island emu, these included taxa found on Kangaroo Island and Tasmania, all of which are now extinct. The smallest taxon, the King Island emu, was confined to a small island situated in the Bass Strait between Tasmania and Victoria, approximately 100 km (62 mi) from both coasts. King Island was once part of the land bridge which connected Tasmania and mainland Australia, but rising sea levels following the last glacial maximum eventually isolated the island. As a result of phenotypic plasticity the King Island emu population possibly underwent a process of insular dwarfism. Emu eggshells were also identified from Flinders Island (in the opposite, eastern end of the Bass Strait) in 2017, possibly representing a distinct taxon.

According to the 2011 genetic study, the close relation between the King Island and mainland emus indicates that the former population was isolated from the latter relatively recently, due to sea level changes in the Bass Strait, as opposed to a founding emu lineage that diverged from the mainland emu far earlier and had subsequently gone extinct on the mainland. Models of sea level change indicate that Tasmania, including King Island, was isolated from the Australian mainland around 14,000 years ago. Up to several thousand years later King Island was then separated from Tasmania. This scenario would suggest that a population ancestral to both the King Island and Tasmanian emu was initially isolated from the mainland taxon, after which the King Island and Tasmanian populations were separated. This, in turn, indicates that the likewise extinct Tasmanian emu is probably as closely related to the mainland emu as is the King Island emu, with both the King Island and Tasmanian emu being more closely related to each other. Fossil emu taxa show an average size between that of the King Island emu and mainland emu. Hence, mainland emus can be regarded as a large or gigantic form.

A 2018 study by Australian geneticist Vicki A. Thomson and colleagues (based on ancient bone, eggshell and feather samples) found that the emus of Kangaroo Island and Tasmania also represented sub-populations of the mainland emu, and therefore belonged in the same species. They also found that the size of the island emus scaled linearly to the size of the islands they inhabited (the King Island emu was the smallest, while the Tasmanian was the largest), while time in isolation did not affect their size. This suggest that island size was the important driver in dwarfism of these emus, probably due to limitation in resources, though the exact effect needs to be confirmed. The little genetic differentiation between island emus indicates their dwarfism evolved rapidly and independently since they became isolated from each other. King Island is 1,100 km2 (420 sq mi), and was isolated from Tasmania for 12,000 years, while 62,400 km2 (24,100 sq mi) Tasmania was itself isolated from mainland Australia for 14,000 years. Kangaroo Island is 4,400 km2 (1,700 sq mi) and was isolated from the mainland 10,000 years ago. A 2020 genetic study of the only known Kangaroo Island emu skin by the French ornithologist Alice Cibois and colleagues also supported retaining the three island emus as subspecies, with the King Island emu as D. n. minor.

## Description

The King Island emu was the smallest type of emu and was about 44% or half of the size of the mainland bird. It was about 87 cm (34 in) tall. According to Péron's interview with the local English sealer Daniel Cooper, the largest specimens were up to 137 cm (4.5 ft) in length, and the heaviest weighed 20 to 23 kg (45 to 50 lb). It had a darker plumage, with extensive black feathers on the neck and head, and blackish feathers on the body, where it was also mixed with brown. The bill and feet were blackish, and the naked skin on the side of the neck was blue. The 2011 genetic study did not find genes commonly associated with melanism in birds, but proposed the dark colouration could be due to alternative genetic or non-genetic factors.

Péron stated there was little difference between the sexes, but that the male was perhaps brighter in colouration and slightly larger. The juveniles were grey, while the chicks were striped like other emus. There were no seasonal variations in plumage. Since the female mainland emus are on average larger than the males, and can turn brighter during the mating season, contrary to the norm in other bird species, the Australian museum curator Stephanie Pfennigwerth suggested that some of these observations may have been based on erroneous conventional wisdom. Hume and Robinson also suggested female King Island emus were larger than the males, and that Cooper could have mistaken brooding males for females when he stated the males were larger.

Subfossil remains of the King Island emu show that the tibia was about 330 mm (13 in) long, and the femur was 180 mm (7 in) long. The pelvis was 280 mm (11 in) long, 64 mm (2.5 in) wide at the front, and 86 mm (3 in) wide at the back. The tarsometatarsus averaged 232 mm (9 in) in length. In males, the tibiotarsus averaged 261 mm (10 in), whereas it averaged 301 mm (12 in) in females. In contrast, the same bones measured 269 mm (10.5 in) and 305 mm (12 in) in the Kangaroo Island emu. Apart from being smaller, the King Island emu differed osteologically from the Kangaroo Island emu in the intertrochlear foramen of the tarsometatarsus usually being fully or partially abridged. The outer trochlea was more incurved towards the middle trochlea in the Kangaroo Island bird, whereas they were parallel in the King Island emu.

The King Island emu and the mainland emu show few morphological differences other than their significant difference in size. Mathews stated that the legs and bill were shorter than those of the mainland emu, yet the toes were nearly of equal length, and therefore proportionally longer. The tarsus of the King Island emu was also three times longer than the culmen, whereas it was four times longer in the mainland emu. Additional traits that supposedly distinguish this bird from the mainland emu have previously been suggested to be the distal foramen of the tarsometatarsus, and the contour of the cranium. However, the distal foramen is known to be variable in the mainland emu showing particular diversity between juvenile and adult forms and is therefore taxonomically insignificant. The same is true of the contour of the cranium, which is more dome-shaped in the King Island emu, a feature that is also seen in juvenile mainland emus.

## Behaviour and ecology

Péron's interview described some aspects of the behaviour of the King Island emu. He wrote that the bird was generally solitary but gathered in flocks of ten to twenty at breeding time, then wandered off in pairs. They ate berries, grass and seaweed, and foraged mainly during morning and evening. They were swift runners, but were apparently slower than the mainland birds, due to being fat. They swam well, but only did so when necessary. They reportedly liked the shade of lagoons and the shoreline, rather than open areas. They used a claw on each wing for scratching themselves. If unable to flee from the hunting dogs of the sealers, they would defend themselves by kicking, which could inflict a great deal of harm.

The English Captain Matthew Flinders did not encounter emus when he visited King Island in 1802, but his naturalist, Robert Brown, examined their dung and noted they had chiefly fed on the berries of Leptecophylla juniperina. An account by English ornithologist John Latham about the "Van Diemen's cassowary" may also refer to the King Island emu, based on the small size described. In addition to a physical description, he stated that they gathered in groups of 70 to 80 individuals in a given location while foraging, behaviour that was exploited by hunters. Hume and colleagues noted that most emu subfossils from King Island were found on the drier, leeward west coast of the island, and though probably due to preservation bias, they suggested that the emus were restricted to coastal and more open inland areas, and not found in the dense interior forests. An 1802 report by the English surveyor Charles Grimes also supported this, stating there were "plenty on the coast–but not inland". The tall, dense eucalypt forests of the island have since been destroyed.

### Breeding

Péron stated that the nest was usually situated near water and on the ground under the shade of a bush. It was constructed of sticks and lined with dead leaves and moss; it was oval in shape and not very deep. He claimed that seven to nine eggs were laid always on 25 and 26 July, but the selective advantage of this breeding synchronisation is unknown. The female incubated the eggs, but the male apparently developed a brood patch, which indicates it contributed as well. The non-incubating parent also stayed by the nest, and the chicks left the nest two to three days after hatching. The eggs were preyed upon by snakes, rats, and quolls. Péron gave the incubation period as five or six weeks, but since the mainland emu incubates for 50 to 56 days, Pfennigwerth pointed out that this may be too short. He stated a mother emu would defend its young from crows with its beak, but this is now known to be strictly male behaviour.

Hume and Robertson compared the eggs of all emu taxa in 2021, and found that the eggs of the island dwarf emus were within or close to the size and smallest volume and mass ranges for mainland birds, with seemingly thinner eggshells. The egg of the mainland emu weighs 1.3 lbs. (0.59 kilograms) and has a volume of about 0.14 gallons (539 milliliters), while those of the King Island emu weighed 1.2 lbs. (0.54 kg) and had a volume of 0.12 gallons (465 mL). The egg mass of the mainland emu accounts for 1.6% of its body mass, whereas the egg mass of the King Island emu accounted for 2.3% of its body mass, even though it was 44% lighter than the mainland bird. Hume and Robertson attempted to explain these findings, and noted that emus and other ratites have precocial juveniles, that is, relatively mature and mobile when they hatch, and appear to have laid their eggs at the same time.

Hume and Robertson suggested the evolutionary advantage for the small emus in retaining large eggs and precocial chicks was driven mainly by limited food resources on their islands. Their chicks had to be large enough to feed on seasonably available food, and possibly to develop thermoregulation sufficient for them to deal with cool temperatures, as is the case for mainland emus and kiwis. The large egg-size and smaller clutch of small emus may have been evolutionary steps towards K selection. The precocial juveniles may also have been an adaptation to predation, and while King Island did not have large carnivores, there was a now extirpated population of very large tiger quolls which could have preyed on emu chicks. If the size of the clutch of King Island emus was large, and not the result of more than one female laying eggs in a single nest, this bird must have devoted an amount of energy to reproduction that was proportionally higher than that of mainland birds. Among living ratites, the rhea is morphometrically similar to the King Island emu, and has a similar breeding strategy.

## Relationship with humans

The emus of King Island were first recorded by Europeans when a party from the British ship Lady Nelson, led by the Scottish explorer John Murray, visited the island in January 1802. Murray noted on 12 January that "they found feathers of emus and a dead one", but some days later they found "woods full of kangaroo, emus, badgers, etc.", and one emu was "caught by the dog about 50 lbs weight and surprisingly fat." The bird was sporadically mentioned by travellers henceforward, but not in detail. Captain Nicolas Baudin visited King Island later in 1802, during an 1800–04 French expedition to map the coast of Australia. Two ships, Le Naturaliste and Le Géographe, were part of the expedition, which also brought along naturalists who described the local wildlife. Péron visited King Island and was the last person to record descriptions of the King Island emu from the wild. At one point, Péron and some of his companions became stranded due to storms and took refuge with some sealers. They were served emu meat, which Péron described in favourable terms as tasting halfway "between that of the turkey-cock and that of the young pig".

Péron did not report seeing any emus on the island himself, which might explain why he described them as being the size of mainland birds. Instead, most of what is known about the King Island emu today stems from a 33-point questionnaire that he used to interview Cooper about the bird. In accordance with a request by the authorities for the expedition to bring back useful plants and animals, Péron asked if the emus could be bred and fattened in captivity, and received a variety of cooking recipes. Cooper sold at least three King Island emus to the French expedition, as well as kangaroos and wombats. Péron's questionnaire remained unpublished until 1899, and very little was therefore known about the bird in life until then.

### Transported specimens

Several emu specimens belonging to the different subspecies were sent to France, both live and dead, as part of the expedition. Some of these exist in European museums today. Le Naturaliste brought one live specimen and one skin of the mainland emu to France in June 1803. Le Géographe collected emus from both King and Kangaroo Island, and at least two live King Island individuals, assumed to be a male and female by some sources, were taken to France in March 1804. This ship also brought skins of five juveniles collected from different islands. Two of these skins, of which the provenance is unknown, are presently kept in Paris and Turin; the rest are lost. In addition to rats, cockroaches, and other inconveniences aboard the ships, the emus were incommoded by the rough weather which caused the ships to shake violently; some died as a result, while others had to be force fed so they did not starve to death. In all, Le Géographe brought 73 live animals of various species back to France.

The two individuals brought to France were first kept in captivity in the menagerie of Empress Josephine, and were moved to the Jardin des Plantes after a year. The "female" died in April 1822, and its skin is now mounted in the Muséum national d'Histoire naturelle of Paris. The "male" died in May 1822, and is preserved as a skeleton in the same museum. A feather of the Paris skin was given to the Tasmanian Museum and Art Gallery, the only confirmed feather belonging to this subspecies currently in Australia. The Paris skin contains several bones, but not the pelvis, which is an indicator of sex, so the supposed female identity is unconfirmed. Péron noted that the small emus brought to France were distinct from those of the mainland, but not that they were distinct from each other, or which island each had come from, so their provenance was unknown for more than a century later.

There is also a skeleton in the Royal Zoological Museum, Florence, which it obtained from France in 1833, but was mislabelled as a cassowary and used by students until correctly identified by Italian zoologist Enrico Hillyer Giglioli in 1900. The skeleton is worn, and several elements are missing, some having been replaced with wooden copies (probably based on those of the Paris skeleton), including the pectoral girdle, the wings, and parts of the legs and skull. Its right metatarsus was damaged during life and had healed incorrectly. It was thought to be a male (and incorrectly that of the Paris skin), but is now known to be a composite of two individuals. A fourth specimen was thought to be kept in the Liverpool Museum, but it may simply be a juvenile mainland emu. Apart from the King Island emu specimens brought to France, a few are also known to have been brought to mainland Australia in 1803, but their fate is unknown.

### Contemporary depictions

Péron's 1807, three-volume account of the expedition, Voyage de découverte aux terres Australes, contains an illustration (plate 36) of "casoars" by Charles-Alexandre Lesueur, who was the resident artist during Baudin's voyage. The caption states the birds shown are from "Ile Decrès", the French name for Kangaroo Island, but there is confusion over what is actually depicted. The two adult birds are labelled as a male and female of the same species, surrounded by juveniles. The family-group shown is improbable, since breeding pairs of the mainland emu split up once the male begins incubating the eggs. Lesueur's preparatory sketches also indicate these may have been drawn after the captive birds in Jardin des Plantes, and not wild ones, which would have been harder to observe for extended periods.

Pfennigwerth has instead proposed that the larger, light-ruffed "male" was actually drawn after a captive Kangaroo Island emu, that the smaller, dark "female" is a captive King Island emu, that the scenario is fictitious, and the sexes of the birds indeterminable. They may instead only have been assumed to be male and female of the same species due to their difference in size. A crooked claw on the "male" has also been interpreted as evidence that it had lived in captivity, and it may also indicate that the depicted specimen is identical to the Kangaroo Island emu skeleton in Paris, which has a deformed toe. The juvenile on the right may have been based on the Paris skin of an approximately five-month-old emu specimen (from either King or Kangaroo Island), which may in turn be the individual that died on board le Geographe during rough weather, and was presumably stuffed there by Lesueur himself. The chicks may instead simply have been based on those of mainland emus, as none are known to have been collected.

### Extinction

The exact cause for the extinction of the King Island emu is unknown. Soon after the bird was discovered, sealers settled on the island because of the abundance of elephant seals. Péron's interview with Cooper suggested that they likely contributed to the demise of the bird by hunting it, and perhaps by starting fires. Péron described how dogs were purpose-trained to hunt down the emus; Cooper even claimed to have killed no fewer than 300 emus himself. Cooper had been on the island for six months, which suggests he killed 50 birds a month. His group of sealers consisted of eleven men as well as his wife, and they alone may have killed 3,600 emus by the time Péron visited them.

Péron explained that the sealers consumed an enormous quantity of meat, and that their dogs killed several animals each day. He also observed such hunting dogs being released on Kangaroo Island, and mused that they might wipe out the entire population of kangaroos there in some years, but he did not express the same sentiment about the emus of King Island. Based on the possibly restricted distribution of the emu to coastal areas, Hume and colleagues suggested this might explain their rapid disappearance, as these areas were easily accessible to sealers. Natural fires may also have played a role. It is probable that the two captive birds in France, which died in 1822, outlived their wild fellows on King Island, and were therefore the last of their kind. Though Péron stated King Island "swarmed" with emus in 1802, they may have become extinct in the wild as early as 1805. They were certainly extinct by 1836, when some English settlers arrived on the island. Elephant seals disappeared from the island around 1819 due to over-hunting.

In 1967, when the King Island emu was still thought to be only known from prehistoric remains, the American ornithologist James Greenway questioned whether they could have been exterminated by a few natives, and speculated that fires started by prehistoric men or lightning may have been responsible. At this time, the mainland emu was also threatened by overhunting, and Greenway cautioned that it could end up sharing the fate of its island relatives if no measures were taken in time.

Extinct subspecies of flightless bird from the Bass Strait island

Species made extinct by human activities


History of timekeeping devices

The history of timekeeping devices dates back to when ancient civilizations first observed astronomical bodies as they moved across the sky. Devices and methods for keeping time have gradually improved through a series of new inventions, starting with measuring time by continuous processes, such as the flow of liquid in water clocks, to mechanical clocks, and eventually repetitive, oscillatory processes, such as the swing of pendulums. Oscillating timekeepers are used in all modern timepieces.

Sundials and water clocks were first used in ancient Egypt from 1500 BC and later by the Babylonians, the Greeks and the Chinese. Incense clocks were being used in China by the 6th century. In the medieval period, Islamic water clocks were unrivalled in their sophistication until the mid-14th century. The hourglass, invented in Europe, was one of the few reliable methods of measuring time at sea.

In medieval Europe, purely mechanical clocks were developed after the invention of the bell-striking alarm, used to signal the correct time to ring monastic bells. The weight-driven mechanical clock controlled by the action of a verge and foliot was a synthesis of earlier ideas from European and Islamic science. Mechanical clocks were a major breakthrough, one notably designed and built by Henry de Vick in c. 1360, which established basic clock design for the next 300 years. Minor developments were added, such as the invention of the mainspring in the early 15th century, which allowed small clocks to be built for the first time.

The next major improvement in clock building, from the 17th century, was the discovery that clocks could be controlled by harmonic oscillators. Leonardo da Vinci had produced the earliest known drawings of a pendulum in 1493–1494, and in 1582 Galileo Galilei had investigated the regular swing of the pendulum, discovering that frequency was only dependent on length, not weight. The pendulum clock, designed and built by Dutch polymath Christiaan Huygens in 1656, was so much more accurate than other kinds of mechanical timekeepers that few verge and foliot mechanisms have survived. Other innovations in timekeeping during this period include inventions for striking clocks, the repeating clock and the deadbeat escapement.

Error factors in early pendulum clocks included temperature variation, a problem tackled during the 18th century by the English clockmakers John Harrison and George Graham. Following the Scilly naval disaster of 1707, after which governments offered a prize to anyone who could discover a way to determine longitude, Harrison built a succession of accurate timepieces, introducing the term chronometer. The electric clock, invented in 1840, was used to control the most accurate pendulum clocks until the 1940s, when quartz timers became the basis for the precise measurement of time and frequency.

The wristwatch, which had been recognised as a valuable military tool during the Boer War, became popular after World War I, in variations including non-magnetic, battery-driven, and solar powered, with quartz, transistors and plastic parts all introduced. Since the early 2010s, smartphones and smartwatches have become the most common timekeeping devices.

The most accurate timekeeping devices in practical use today are atomic clocks, which can be accurate to a few billionths of a second per year and are used to calibrate other clocks and timekeeping instruments.

## Continuous timekeeping devices

Ancient civilizations observed astronomical bodies, often the Sun and Moon, to determine time. According to the historian Eric Bruton, Stonehenge is likely to have been the Stone Age equivalent of an astronomical observatory, used for seasonal and annual events such as equinoxes or solstices. As megalithic civilizations left no recorded history, little is known of their timekeeping methods.

Mesoamericans modified their usual vigesimal (base-20) counting system when dealing with calendars to produce a 360-day year. Aboriginal Australians understood the movement of objects in the sky well, and used their knowledge to construct calendars and aid navigation; most Aboriginal cultures had seasons that were well-defined and determined by natural changes throughout the year, including celestial events. Lunar phases were used to mark shorter periods of time; the Yaraldi of South Australia being one of the few people recorded as having a way to measure time during the day, which was divided into seven parts using the position of the Sun.

All timekeepers before the 13th century relied upon methods that used something that moved continuously. No early method of keeping time changed at a steady rate. Devices and methods for keeping time have improved continuously through a long series of new inventions and ideas.

### Shadow clocks and sundials

The first devices used for measuring the position of the Sun were shadow clocks, which later developed into the sundial. The oldest of all known sundials dates back to c. 1500 BC (during the 19th Dynasty), and was discovered in the Valley of the Kings in 2013. Obelisks could indicate whether it was morning or afternoon, as well as the summer and winter solstices. A kind of shadow clock was developed c. 500 BC that was similar in shape to a bent T-square. It measured the passage of time by the shadow cast by its crossbar, and was oriented eastward in the mornings, and turned around at noon, so it could cast its shadow in the opposite direction.

A sundial is referred to in the Bible, in 2 Kings 20:9–11, when Hezekiah, king of Judea during the 8th century BC, is recorded as being healed by the prophet Isaiah and asks for a sign that he would recover:

> And Isaiah said, This sign shalt thou have of the Lord, that the Lord will do the thing that he hath spoken: shall the shadow go forward ten degrees, or go back ten degrees? And Hezekiah answered, It is a light thing for the shadow to go down ten degrees: nay, but let the shadow return backward ten degrees. And Isaiah the prophet cried unto the Lord: and he brought the shadow ten degrees backward, by which it had gone down in the dial of Ahaz.

A clay tablet from the late Babylonian period describes the lengths of shadows at different times of the year. The Babylonian writer Berossos () is credited by the Greeks with the invention of a hemispherical sundial hollowed out of stone; the path of the shadow was divided into 12 parts to mark the time. Greek sundials evolved to become highly sophisticated—Ptolemy's Analemma, written in the 2nd century AD, used an early form of trigonometry to derive the position of the Sun from data such as the hour of day and the geographical latitude. The Romans borrowed the idea of the sundial from the Greeks. The military commander Pliny the Elder recorded that the first sundial in Rome arrived in 264 BC, looted from Catania in Sicily; according to him, it gave the incorrect time for a century, until the markings and angle appropriate for Rome's latitude were used.

According to the German historian of astronomy Ernst Zinner, sundials were developed during the 13th century with scales that showed equal hours. The first based on polar time appeared in Germany c. 1400; an alternative theory proposes that a Damascus sundial measuring in polar time can be dated to 1372. European treatises on sundial design appeared c. 1500.

An Egyptian method of determining the time during the night, used from at least 600 BC, was a type of plumb-line called a merkhet. A north–south meridian was created using two merkhets aligned with Polaris, the north pole star. The time was determined by observing particular stars as they crossed the meridian.

### Water clocks

The oldest description of a clepsydra, or water clock, is from the tomb inscription of an early 18th Dynasty (c. 1500 BC) Egyptian court official named Amenemhet, who is identified as its inventor. It is assumed that the object described on the inscription is a bowl with markings to indicate the time. The oldest surviving water clock was found in the tomb of pharaoh Amenhotep III (c. 1417–1379 BC). There are no recognised examples in existence of outflowing water clocks from ancient Mesopotamia, but written references have survived.

The introduction of the water clock to China, perhaps from Mesopotamia, occurred as far back as the 2nd millennium BC, during the Shang dynasty, and at the latest by the 1st millennium BC. Around 550 AD, Yin Kui (殷蘷) was the first in China to write of the overflow or constant-level tank in his book "Lou ke fa (漏刻法)". Around 610, two Sui dynasty inventors, Geng Xun (耿詢) and Yuwen Kai (宇文愷), created the first balance clepsydra, with standard positions for the steelyard balance. In 721 the mathematician Yi Xing and government official Liang Lingzan regulated the power of the water driving an astronomical clock, dividing the power into unit impulses so that motion of the planets and stars could be duplicated. In 976, the Song dynasty astronomer Zhang Sixun addressed the problem of the water in clepsydrae freezing in cold weather when he replaced the water with liquid mercury. A water-powered astronomical clock tower was built by the polymath Su Song in 1088, which featured the first known endless power-transmitting chain drive.

The Greek philosophers Anaxagoras and Empedocles both referred to water clocks that were used to enforce time limits or measure the passing of time. The Athenian philosopher Plato is supposed to have invented an alarm clock that used lead balls cascading noisily onto a copper platter to wake his students.

A problem with most clepsydrae was the variation in the flow of water due to the change in fluid pressure, which was addressed from 100 BC when the clock's water container was given a conical shape. They became more sophisticated when innovations such as gongs and moving mechanisms were included. There is evidence that the 1st century BC Tower of the Winds in Athens once had eight sundials, a water clock, and a wind vane. In Greek tradition, clepsydrae were used in court, a practise later adopted by the Ancient Romans.

The first geared clock, invented in the 11th century by the Arab engineer Ibn Khalaf al-Muradi in Islamic Iberia, was a water clock that employed both segmental and epicyclic gearing. Islamic water clocks, which used complex gear trains and included arrays of automata, were unrivalled in their sophistication until the mid-14th century. Liquid-driven mechanisms (using heavy floats and a constant-head system) were developed that enabled water clocks to work at a slower rate.

The 12th-century Jayrun Water Clock at the Umayyad Mosque in Damascus was constructed by Muhammad al-Sa'ati, and was later described by his son Ridwan ibn al-Sa'ati in his On the Construction of Clocks and their Use (1203). A sophisticated water-powered astronomical clock was described by Al-Jazari in his treatise on machines, written in 1206. This castle clock was about 11 metres (36 ft) high, and included a display of the zodiac and the solar and lunar paths, and doors that opened on the hour, to reveal a mannequin. In 1235, a water-powered clock that "announced the appointed hours of prayer and the time both by day and by night" stood in the entrance hall of the Mustansiriya Madrasah in Baghdad.

### Chinese incense clocks

Incense clocks were first used in China around the 6th century, mainly for religious purposes, but also for social gatherings or by scholars. Due to their frequent use of Devanagari characters, American sinologist Edward H. Schafer has speculated that incense clocks were invented in India. As incense burns evenly and without a flame, the clocks were safe for indoor use. To mark different hours, differently scented incenses (made from different recipes) were used.

The incense sticks used could be straight or spiralled; the spiralled ones were intended for long periods of use, and often hung from the roofs of homes and temples. Some clocks were designed to drop weights at even intervals.

Incense seal clocks had a disk etched with one or more grooves, into which incense was placed. The length of the trail of incense, directly related to the size of the seal, was the primary factor in determining how long the clock would last; to burn 12 hours an incense path of around 20 metres (66 ft) has been estimated. The gradual introduction of metal disks, most likely beginning during the Song dynasty, allowed craftsmen to more easily create seals of different sizes, design and decorate them more aesthetically, and vary the paths of the grooves, to allow for the changing length of the days in the year. As smaller seals became available, incense seal clocks grew in popularity and were often given as gifts.

### Astrolabes

Sophisticated timekeeping astrolabes with geared mechanisms were made in Persia. Examples include those built by the polymath Abū Rayhān Bīrūnī in the 11th century and the astronomer Muhammad ibn Abi Bakr al‐Farisi in c.1221. A brass and silver astrolabe (which also acts as a calendar) made in Isfahan by al‐Farisi is the earliest surviving machine with its gears still intact. Openings on the back of the astrolabe depict the lunar phases and gives the Moon's age; within a zodiacal scale are two concentric rings that show the relative positions of the Sun and the Moon.

Muslim astronomers constructed a variety of highly accurate astronomical clocks for use in their mosques and observatories, such as the astrolabic clock by Ibn al-Shatir in the early 14th century.

### Candle clocks and hourglasses

One of the earliest references to a candle clock is in a Chinese poem, written in 520 by You Jianfu, who wrote of the graduated candle being a means of determining time at night. Similar candles were used in Japan until the early 10th century.

The invention of the candle clock was attributed by the Anglo-Saxons to Alfred the Great, king of Wessex (r. 871–889), who used six candles marked at intervals of one inch (25 mm), each made from 12 pennyweights of wax, and made to be 12 centimetres (4.7 in) high and of a uniform thickness.

The 12th century Muslim inventor Al-Jazari described four different designs for a candle clock in his book Book of Knowledge of Ingenious Mechanical Devices. His so-called "scribe" candle clock was invented to mark the passing of 14 hours of equal length: a precisely engineered mechanism caused a candle of specific dimensions to be slowly pushed upwards, which caused an indicator to move along a scale. Every hour a small ball emerged from the beak of a bird.

The hourglass was one of the few reliable methods of measuring time at sea, and it has been speculated that it was used on board ships as far back as the 11th century, when it would have complemented the compass as an aid to navigation. The earliest unambiguous evidence of the use an hourglass appears in the painting Allegory of Good Government, by the Italian artist Ambrogio Lorenzetti, from 1338.

The Portuguese navigator Ferdinand Magellan used 18 hourglasses on each ship during his circumnavigation of the globe in 1522. Though used in China, the hourglass's history there is unknown, but does not seem to have been used before the mid-16th century, as the hourglass implies the use of glassblowing, then an entirely European and Western art.

From the 15th century onwards, hourglasses were used in a wide range of applications at sea, in churches, in industry, and in cooking; they were the first dependable, reusable, reasonably accurate, and easily constructed time-measurement devices. The hourglass took on symbolic meanings, such as that of death, temperance, opportunity, and Father Time, usually represented as a bearded, old man.

## History of early oscillating devices in timekeepers

The English word clock first appeared in Middle English as clok, cloke, or clokke. The origin of the word is not known for certain; it may be a borrowing from French or Dutch, and can perhaps be traced to the post-classical Latin clocca ('bell'). 7th century Irish and 9th century Germanic sources recorded clock as meaning 'bell'.

Judaism, Christianity and Islam all had times set aside for prayer, although Christians alone were expected to attend prayers at specific hours of the day and night—what the historian Jo Ellen Barnett describes as "a rigid adherence to repetitive prayers said many times a day". The bell-striking alarms warned the monk on duty to toll the monastic bell. His alarm was a timer that used a form of escapement to ring a small bell. This mechanism was the forerunner of the escapement device found in the mechanical clock.

### 13th century

The first innovations to improve on the accuracy of the hourglass and the water clock occurred in the 10th century, when attempts were made to slow their rate of flow using friction or the force of gravity. The earliest depiction of a clock powered by a hanging weight is from the Bible of St Louis, an illuminated manuscript that shows a clock being slowed by water acting on a wheel. The illustration seems to show that weight-driven clocks were invented in western Europe. A treatise written by Robertus Anglicus in 1271 shows that medieval craftsmen were attempting to design a purely mechanical clock (i.e. only driven by gravity) during this period. Such clocks were a synthesis of earlier ideas derived from European and Islamic science, such as gearing systems, weight drives, and striking mechanisms.

In 1250, the artist Villard de Honnecourt illustrated a device that was the step towards the development of the escapement. Another forerunner of the escapement was the horologia nocturna, which used an early kind of verge mechanism to operate a knocker that continuously struck a bell. The weight-driven clock was probably a Western European invention, as a picture of a clock shows a weight pulling an axle around, its motion slowed by a system of holes that slowly released water. In 1271, the English astronomer Robertus Anglicus wrote of his contemporaries that they were in the process of developing a form of mechanical clock.

### 14th century

The invention of the verge and foliot escapement in c.1275 was one of the most important inventions in both the history of the clock and the history of technology. It was the first type of regulator in horology. A verge, or vertical shaft, is forced to rotate by a weight-driven crown wheel, but is stopped from rotating freely by a foliot. The foliot, which cannot vibrate freely, swings back and forth, which allows a wheel to rotate one tooth at a time. Although the verge and foliot was an advancement on previous timekeepers, it was impossible to avoid fluctuations in the beat caused by changes in the applied forces—the earliest mechanical clocks were regularly reset using a sundial.

At around the same time as the invention of the escapement, the Florentine poet Dante Alighieri used clock imagery to depict the souls of the blessed in Paradiso, the third part of the Divine Comedy, written in the early part of the 14th century. It may be the first known literary description of a mechanical clock. There are references to house clocks from 1314 onwards; by 1325 the development of the mechanical clock can be assumed to have occurred.

Large mechanical clocks were built that were mounted in towers so as to ring the bell directly. The tower clock of Norwich Cathedral constructed c. 1273 (reference to a payment for a mechanical clock dated to this year) is the earliest such large clock known. The clock has not survived. The first clock known to strike regularly on the hour, a clock with a verge and foliot mechanism, is recorded in Milan in 1336. By 1341, clocks driven by weights were familiar enough to be able to be adapted for grain mills, and by 1344 the clock in London's Old St Paul's Cathedral had been replaced by one with an escapement. The foliot was first illustrated by Dondi in 1364, and mentioned by the court historian Jean Froissart in 1369.

The most famous example of a timekeeping device during the medieval period was a clock designed and built by the clockmaker Henry de Vick in c.1360, which was said to have varied by up to two hours a day. For the next 300 years, all the improvements in timekeeping were essentially developments based on the principles of de Vick's clock. Between 1348 and 1364, Giovanni Dondi dell'Orologio, the son of Jacopo Dondi, built a complex astrarium in Florence.

During the 14th century, striking clocks appeared with increasing frequency in public spaces, first in Italy, slightly later in France and England—between 1371 and 1380, public clocks were introduced in over 70 European cites. Salisbury Cathedral clock, dating from about 1386, is one of the oldest working clocks in the world, and may be the oldest; it still has most of its original parts. The Wells Cathedral clock, built in 1392, is unique in that it still has its original medieval face. Above the clock are figures which hit the bells, and a set of jousting knights who revolve around a track every 15 minutes.

### Later developments

The invention of the mainspring in the early 15th century—a device first used in locks and for flintlocks in guns— allowed small clocks to be built for the first time. The need for an escapement mechanism that steadily controlled the release of the stored energy, led to the development of two devices, the stackfreed (which although invented in the 15th century can be documented no earlier than c.1535) and the fusee, which first originated from medieval weapons such as the crossbow. There is a fusee in the earliest surviving spring-driven clock, a chamber clock made for Philip the Good in c. 1430. Leonardo da Vinci, who produced the earliest known drawings of a pendulum in 1493–1494, illustrated a fusee in c. 1500, a quarter of a century after the coiled spring first appeared.

Clock towers in Western Europe in the Middle Ages struck the time. Early clock dials showed hours; a clock with a minutes dial is mentioned in a 1475 manuscript. During the 16th century, timekeepers became more refined and sophisticated, so that by 1577 the Danish astronomer Tycho Brahe was able to obtain the first of four clocks that measured in seconds, and in Nuremberg, the German clockmaker Peter Henlein was paid for making what is thought to have been the earliest example of a watch, made in 1524. By 1500, the use of the foliot in clocks had begun to decline. The oldest surviving spring-driven clock is a device made by Bohemian Jacob Zech [cs] in 1525. The first person to suggest travelling with a clock to determine longitude, in 1530, was the Dutch instrument maker Gemma Frisius. The clock would be set to the local time of a starting point whose longitude was known, and the longitude of any other place could be determined by comparing its local time with the clock time.

The Ottoman engineer Taqi ad-Din described a weight-driven clock with a verge-and-foliot escapement, a striking train of gears, an alarm, and a representation of the Moon's phases in his book The Brightest Stars for the Construction of Mechanical Clocks (Al-Kawākib al-durriyya fī wadh' al-bankāmat al-dawriyya), written around 1556. Jesuit missionaries brought the first European clocks to China as gifts.

The Italian polymath Galileo Galilei is thought to have first realized that the pendulum could be used as an accurate timekeeper after watching the motion of suspended lamps at Pisa Cathedral. In 1582, he investigated the regular swing of the pendulum, and discovered that this was only dependent on its length. Galileo never constructed a clock based on his discovery, but prior to his death he dictated instructions for building a pendulum clock to his son, Vincenzo.

## Era of precision timekeeping

### Pendulum clocks

The first accurate timekeepers depended on the phenomenon known as harmonic motion, in which the restoring force acting on an object moved away from its equilibrium position—such as a pendulum or an extended spring—acts to return the object to that position, and causes it to oscillate. Harmonic oscillators can be used as accurate timekeepers as the period of oscillation does not depend on the amplitude of the motion—and so it always takes the same time to complete one oscillation. The period of a harmonic oscillator is completely dependent on the physical characteristics of the oscillating system and not the starting conditions or the amplitude.

The period when clocks were controlled by harmonic oscillators was the most productive era in timekeeping. The first invention of this type was the pendulum clock, which was designed and built by Dutch polymath Christiaan Huygens in 1656. Early versions erred by less than one minute per day, and later ones only by 10 seconds, very accurate for their time. Dials that showed minutes and seconds became common after the increase in accuracy made possible by the pendulum clock. Brahe used clocks with minutes and seconds to observe stellar positions. The pendulum clock outperformed all other kinds of mechanical timekeepers to such an extent that these were usually refitted with a pendulum—a task that could be done without difficulty—so that few verge escapement devices have survived in their original form.

The first pendulum clocks used a verge escapement, which required wide swings of about 100° and so had short, light pendulums. The swing was reduced to around 6° after the invention of the anchor mechanism enabled the use of longer, heavier pendulums with slower beats that had less variation, as they more closely resembled simple harmonic motion, required less power, and caused less friction and wear. The first known anchor escapement clock was built by the English clockmaker William Clement in 1671 for King's College, Cambridge, now in the Science Museum, London. The anchor escapement originated with Hooke, although it has been argued that it was invented by Clement, or the English clockmaker Joseph Knibb.

The Jesuits made major contributions to the development of pendulum clocks in the 17th and 18th centuries, having had an "unusually keen appreciation of the importance of precision". In measuring an accurate one-second pendulum, for example, the Italian astronomer Father Giovanni Battista Riccioli persuaded nine fellow Jesuits "to count nearly 87,000 oscillations in a single day". They served a crucial role in spreading and testing the scientific ideas of the period, and collaborated with Huygens and his contemporaries.

Huygens first used a clock to calculate the equation of time (the difference between the apparent solar time and the time given by a clock), publishing his results in 1665. The relationship enabled astronomers to use the stars to measure sidereal time, which provided an accurate method for setting clocks. The equation of time was engraved on sundials so that clocks could be set using the Sun. In 1720, Joseph Williamson claimed to have invented a clock that showed solar time, fitted with a cam and differential gearing, so that the clock indicated true solar time.

Other innovations in timekeeping during this period include the invention of the rack and snail striking mechanism for striking clocks by the English mechanician Edward Barlow, the invention by either Barlow or Daniel Quare, a London clock-maker, in 1676 of the repeating clock that chimes the number of hours or minutes, and the deadbeat escapement, invented around 1675 by the astronomer Richard Towneley.

Paris and Blois were the early centres of clockmaking in France, and French clockmakers such as Julien Le Roy, clockmaker of Versailles, were leaders in case design and ornamental clocks. Le Roy belonged to the fifth generation of a family of clockmakers, and was described by his contemporaries as "the most skillful clockmaker in France, possibly in Europe". He invented a special repeating mechanism which improved the precision of clocks and watches, a face that could be opened to view the inside clockwork, and made or supervised over 3,500 watches during his career of almost five decades, which ended with his death in 1759. The competition and scientific rivalry resulting from his discoveries further encouraged researchers to seek new methods of measuring time more accurately.

Any inherent errors in early pendulum clocks were smaller than other errors caused by factors such as temperature variation. In 1729 the Yorkshire carpenter and self-taught clockmaker John Harrison invented the gridiron pendulum, which used at least three metals of different lengths and expansion properties, connected so as to maintain the overall length of the pendulum when it is heated or cooled by its surroundings. In 1781 the clockmaker George Graham compensated for temperature variation in an iron pendulum by using a bob made from a glass jar of mercury—a liquid metal at room temperature that expands faster than glass. More accurate versions of this innovation contained the mercury in thinner iron jars to make them more responsive. This type of temperature compensating pendulum was improved still further when the mercury was contained within the rod itself, which allowed the two metals to be thermally coupled more tightly. In 1895, the invention of invar, an alloy made from iron and nickel that expands very little, largely eliminated the need for earlier inventions designed to compensate for the variation in temperature.

Between 1794 and 1795, in the aftermath of the French Revolution, the French government mandated the use of decimal time, with a day divided into 10 hours of 100 minutes each. A clock in the Palais des Tuileries kept decimal time as late as 1801.

### Marine chronometer

After the Scilly naval disaster of 1707, in which four ships were wrecked as a result of navigational mistakes, the British government offered a prize of £20,000, equivalent to millions of pounds today, for anyone who could determine the longitude to within 50 kilometres (31 mi) at a latitude just north of the equator. The position of a ship at sea could be determined to within 100 kilometres (62 mi) if a navigator could refer to a clock that lost or gained less than about six seconds per day. Proposals were examined by a newly created Board of Longitude. Among the many people who attempted to claim the prize was the Yorkshire clockmaker Jeremy Thacker, who first used the term chronometer in a pamphlet published in 1714. Huygens built the first sea clock, designed to remain horizontal aboard a moving ship, but that stopped working if the ship moved suddenly.

In 1715, at the age of 22, Harrison had used his carpentry skills to construct a wooden eight-day clock. His clocks had innovations that included the use of wooden parts to remove the need for additional lubrication (and cleaning), rollers to reduce friction, a new kind of escapement, and the use of two different metals to reduce the problem of expansion caused by temperature variation. He travelled to London to seek assistance from the Board of Longitude in making a sea clock. He was sent to visit Graham, who assisted Harrison by arranging to finance his work to build a clock. After 30 years, his device, now named "H1" was built and in 1736 it was tested at sea. Harrison then went on to design and make two other sea clocks, "H2" (completed in around 1739) and "H3", both of which were ready by 1755.

Harrison made two watches, "H4" and "H5". Eric Bruton, in his book The History of Clocks and Watches, has described H4 as "probably the most remarkable timekeeper ever made". After the completion of its sea trials during the winter of 1761–1762 it was found that it was three times more accurate than was needed for Harrison to be awarded the Longitude prize.

### Electric clocks

In 1815, the prolific English inventor Francis Ronalds produced the forerunner of the electric clock, the electrostatic clock. It was powered with dry piles, a high voltage battery with extremely long life but the disadvantage of its electrical properties varying according to the air temperature and humidity. He experimented with ways of regulating the electricity and his improved devices proved to be more reliable.

In 1840 the Scottish clock and instrument maker Alexander Bain, first used electricity to sustain the motion of a pendulum clock, and so can be credited with the invention of the electric clock. On January 11, 1841, Bain and the chronometer maker John Barwise took out a patent describing a clock with an electromagnetic pendulum. The English scientist Charles Wheatstone, whom Bain met in London to discuss his ideas for an electric clock, produced his own version of the clock in November 1840, but Bain won a legal battle to establish himself as the inventor.

In 1857, the French physicist Jules Lissajous showed how an electric current can be used to vibrate a tuning fork indefinitely, and was probably the first to use the invention as a method for accurately measuring frequency. The piezoelectric properties of crystalline quartz were discovered by the French physicist brothers Jacques and Pierre Curie in 1880.

The most accurate pendulum clocks were controlled electrically. The Shortt–Synchronome clock, an electrical driven pendulum clock designed in 1921, was the first clock to be a more accurate timekeeper than the Earth itself.

A succession of innovations and discoveries led to the invention of the modern quartz timer. The vacuum tube oscillator was invented in 1912. An electrical oscillator was first used to sustain the motion of a tuning fork by the British physicist William Eccles in 1919; his achievement removed much of the damping associated with mechanical devices and maximised the stability of the vibration's frequency. The first quartz crystal oscillator was built by the American engineer Walter G. Cady in 1921, and in October 1927 the first quartz clock was described by Joseph Horton and Warren Marrison at Bell Telephone Laboratories. The following decades saw the development of quartz clocks as precision time measurement devices in laboratory settings—the bulky and delicate counting electronics, built with vacuum tubes, limited their practical use elsewhere. In 1932, a quartz clock able to measure small weekly variations in the rotation rate of the Earth was developed. Their inherent physical and chemical stability and accuracy has resulted in the subsequent proliferation, and since the 1940s they have formed the basis for precision measurements of time and frequency worldwide.

## Development of the watch

The first wristwatches were made in the 16th century. Elizabeth I of England had made an inventory in 1572 of the watches she acquired, all of which were considered to be part of her jewellery collection. The first pocketwatches were inaccurate, as their size precluded them from having sufficiently well-made moving parts. Unornamented watches began to appear in c. 1625.

Dials that showed minutes and seconds became common after the increase in accuracy made possible by the balance spring (or hairspring). Invented separately in 1675 by Huygens and Hooke, it enabled the oscillations of the balance wheel to have a fixed frequency. The invention resulted in a great advance in the accuracy of the mechanical watch, from around half an hour to within a few minutes per day. Some dispute remains as to whether the balance spring was first invented by Huygens or by Hooke; both scientists claimed to have come up with the idea of the balance spring first. Huygens' design for the balance spring is the type used in virtually all watches up to the present day.

Thomas Tompion was one of the first clockmakers to recognise the potential of the balance spring and use it successfully in his pocket watches; the improved accuracy enabled watches to perform as well as they are generally used today, as a second hand to be added to the face, a development that occurred during the 1690s. The concentric minute hand was an earlier invention, but a mechanism was devised by Quare that enabled the hands to be actuated together. Nicolas Fatio de Duillier, a Swiss natural philosopher, is credited with the design of the first jewel bearings in watches in 1704.

Other notable 18th-century English horologists include John Arnold and Thomas Earnshaw, who devoted their careers to constructing high-quality chronometers and so-called 'deck watches', smaller versions of the chronometer that could be kept in a pocket.

### Military use of the watch

Watches were worn during the Franco-Prussian War (1870–1871), and by the time of the Boer War (1899–1902), watches had been recognised as a valuable tool. Early models were essentially standard pocket watches fitted to a leather strap, but, by the early 20th century, manufacturers began producing purpose-built wristwatches. In 1904, Alberto Santos-Dumont, an early aviator, asked his friend the French watchmaker Louis Cartier to design a watch that could be useful during his flights.

During World War I, wristwatches were used by artillery officers. The so-called trench watch, or 'wristlets' were practical, as they freed up one hand that would normally be used to operate a pocket watch, and became standard equipment. The demands of trench warfare meant that soldiers needed to protect the glass of their watches, and a guard in the form of a hinged cage was sometimes used. The guard was designed to allow the numerals to be read easily, but it obscured the hands—a problem that was solved after the introduction of shatter-resistant Plexiglass in the 1930s. Prior to the advent of its military use, the wristwatch was typically only worn by women, but during World War I they became symbols of masculinity and bravado.

### Modern watches

Fob watches were starting to be replaced at the turn of the 20th century. The Swiss, who were neutral throughout World War I, produced wristwatches for both sides of the conflict. The introduction of the tank influenced the design of the Cartier Tank watch, and the design of watches during the 1920s was influenced by the Art Deco style. The automatic watch, first introduced with limited success in the 18th century, was reintroduced in the 1920s by the English watchmaker John Harwood. After he went bankrupt in 1929, restrictions on automatic watches were lifted and companies such as Rolex were able to produce them. In 1930, Tissot produced the first ever non-magnetic wristwatch.

The first battery-driven watches were developed in the 1950s. High quality watches were produced by firms such as Patek Philippe, an example made in 1933, an example being a Patek Philippe ref. 1518, possibly the most complicated wristwatch ever made in stainless steel, which fetched a world record price in 2016 when it was sold at auction for \$11,136,642.

The manual winding Speedmaster Professional or "Moonwatch" was worn during the first United States spacewalk as part of NASA's Gemini 4 mission and was the first watch worn by an astronaut walking on the Moon during the Apollo 11 mission. In 1969, Seiko produced the world's first quartz wristwatch, the Astron.

During the 1970s, the introduction of digital watches made using transistors and plastic parts enabled companies to reduce their work force. By the 1970s, many of those firms that maintained more complicated metalworking techniques had gone bankrupt.

Smartwatches, essentially wearable computers in the form of watches, were introduced to the market in the early 21st century.

## Atomic clocks

Atomic clocks are the most accurate timekeeping devices in practical use today. Accurate to within a few seconds over many thousands of years, they are used to calibrate other clocks and timekeeping instruments. The U.S. National Bureau of Standards (NBS, now National Institute of Standards and Technology (NIST)) changed the way it based the time standard of the United States from quartz to atomic clocks in the 1960s.

The idea of using atomic transitions to measure time was first suggested by the British scientist Lord Kelvin in 1879, although it was only in the 1930s with the development of magnetic resonance that there was a practical method for measuring time in this way. A prototype ammonia maser device was built in 1948 at NIST. Although less accurate than existing quartz clocks, it served to prove the concept of an atomic clock.

The first accurate atomic clock, a caesium standard based on a certain transition of the caesium-133 atom, was built by the English physicist Louis Essen in 1955 at the National Physical Laboratory in London. It was calibrated by the use of the astronomical time scale ephemeris time (ET).

In 1967 the International System of Units (SI) standardized its unit of time, the second, on the properties of caesium. The SI defined the second as 9,192,631,770 cycles of the radiation which corresponds to the transition between two electron spin energy levels of the ground state of the <sup>133</sup>Cs atom. The caesium atomic clock maintained by NIST is accurate to 30 billionths of a second per year. Atomic clocks have employed other elements, such as hydrogen and rubidium vapor, offering greater stability (in the case of hydrogen clocks) and smaller size, lower power consumption, and thus lower cost (in the case of rubidium clocks).

## See also

- Clock synchronization
- Clockmaker
- Coordinated Universal Time (UTC)
- History of timekeeping devices in Egypt
- Quartz crisis
- Seconds pendulum
- Time metrology
- Time standard
- Timeline of time measurement inventions
- Watchmaker

## Explanatory notes