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.
Billy Gladstone
Among his inventions is a rare jazz instrument similar to the Bock-a-da-bock, a hand-held cymbal apparatus called the “Ludwig Gladstone Cymbal” when it was introduced by the Ludwig Drum Company in 1927. In 1929 the Leedy Drum Company listed it in their catalogue as the “Hand Sock Cymbals.” Gladstone was granted a patent September 27, 1927, for his "Operating Device for Cymbals," his first commercially accepted patent (his previous patents were not mass-produced). This launched an illustrious career as an inventor of percussion and non-percussion items. On April 21, 1931 Gladstone was awarded a patent for a percussion musical instrument. The patent number is 1,801,422.