Guidonian hand
In Medieval music, the Guidonian hand was a mnemonic device used to assist singers in learning to sight-sing. Some form of the device may have been used by Guido of Arezzo, a medieval music theorist who wrote a number of treatises, including one instructing singers in sightreading. The hand occurs in some manuscripts before Guido's time as a tool to find the semitone; it does not have the depicted form until the 12th century. Sigebertus Gemblacensis in 1105–10 did describe Guido using the joints of the hand to aid in teaching his hexachord. The Guidonian hand is closely linked with Guido's new ideas about how to learn music, including the use of hexachords, and the first known Western use of solfege.
Guillotine
A committee was formed under Antoine Louis, physician to the King and Secretary to the Academy of Surgery. Guillotin was also on the committee. The group was influenced by the Italian Mannaia (or Mannaja: which had been used ever since Roman times), the Scottish Maiden and the Halifax Gibbet, which was fitted with an axe head weighing 7 pounds 12 ounces (3.5 kg). While these prior instruments usually crushed the neck or used blunt force to take off a head, devices also usually used a crescent blade and a lunette (a hinged two part yoke to immobilize the victim's neck).