Initially, only the day was divided into 12 seasonal hours and the night into 3 or 4 night watches.By the Hellenistic period the night was also divided into 12 hours. The day-and-night (νυχθήμερον) was probably first divided into twenty-four hours by Hipparchus of Nicaea. The Greek astronomer Andronicus of Cyrrhus oversaw the construction of a horologion called the Tower of the Winds in Athens during the first century BCE. This structure tracked a 24-hour day using both sundials and mechanical hour indicators.The canonical hours were introduced to early Christianity  from Second Temple Judaism. By AD 60, the Didache recommends disciples to pray the Lords Prayer three times a day; this practice found its way into the canonical hours as well. By the second and third centuries, such Church Fathers as Clement of Alexandria, Origen, and Tertullian wrote of the practice of Morning and Evening Prayer, and of the prayers at the third, sixth and ninth hours. In the early church, during the night before every feast, a vigil was kept. The word "Vigils", at first applied to the Night Office, comes from a Latin source, namely the Vigiliae or nocturnal watches or guards of the soldiers. The night from six oclock in the evening to six oclock in the morning was divided into four watches or vigils of three hours each, the first, the second, the third, and the fourth vigil.The Horae were originally personifications of seasonal aspects of nature, not of the time of day.
Chondrocalcinosis or cartilage calcification is calcification (accumulation of calcium salts) in hyaline cartilage and/or fibrocartilage. It can be seen on radiography. Causes
Buildup of calcium phosphate in the ankle joints has been found in about 50% of the general population, and may be associated with osteoarthritis.Another common cause of chondrocalcinosis is calcium pyrophosphate dihydrate crystal deposition disease (CPPD). CPPD is estimated to affect 4% to 7% of the adult populations of Europe and the United States. Previous studies have overestimated the prevalence by simply estimating the prevalence of chondrocalcinosis regardless of cause.A magnesium deficiency may cause chondrocalcinosis, and magnesium supplementation may reduce or alleviate symptoms. In some cases, arthritis from injury can cause chondrocalcinosis. Other causes of chondrocalcinosis include:
Hypercalcaemia, especially when caused by hyperparathyroidism
Arthritis
Pseudogout
Wilson disease
Hemochromatosis
Ochronosis
Hypophosphatasia
Hypothyroidism
Hyperoxalemia
Acromegaly
Gitelman syndrome

Diagnosis
Chondrocalcinosis can be visualized on projectional radiography, CT scan, MRI, US, and nuclear medicine. CT scans and MRIs show calcific masses (usually within the ligamentum flavum or joint capsule), however radiography is more successful. At ultrasound, chondrocalcinosis may be depicted as echogenic foci with no acoustic shadow within the hyaline cartilage. As with most conditions, chondrocalcinosis can present with similarity to other diseases such as ankylosing spondylitis and gout. == References ==