Guido of Arezzo
In the 12th century, a development in teaching and learning music in a more efficient manner had arisen. Guido of Arezzo's alleged development of the Guidonian hand, more than a hundred years after his death, allowed for musicians to label a specific joint or fingertip with the gamut (also referred to as the hexachord in the modern era). Using specific joints of the hand and fingertips transformed the way one would learn and memorize solmization syllables. Not only did the Guidonian hand become a standard use in preparing music in the 12th century, its popularity grew more widespread well into the 17th and 18th century. The knowledge and use of the Guidonian hand would allow a musician to simply transpose, identify intervals, and aid in use of notation and the creation of new music. Musicians were able to sing and memorize longer sections of music and counterpoint during performances and the amount of time spent diminished dramatically.
Hand of God (art)
In Eastern Orthodox icons the hand remained in use far longer than in the Western church, and is still found in modern icons, normally emerging from circular bands. Apart from the narrative scenes mentioned above it is especially often found in icons of military saints, and in some Russian icons is identified by the usual inscription as belonging to Jesus Christ. In other versions of the same composition a small figure of Christ of about the same size as the hand takes its place, which is also seen in many Western works from about 1000 onwards.
The earliest surviving icon of the Virgin Mary, of about 600 from Saint Catherine's Monastery, has an often overlooked hand, suggesting to Robin Cormack that the emphasis of the subject is on the Incarnation rather than a simple Virgin and Child. Another of the very few major Eastern works showing the Virgin from before the Byzantine iconoclasm, an apse mosaic (lost in 1922) from Nicaea, also shows the hand above a standing Virgin. Few similar uses of the hand are seen in later Virgins, though the iconographically adventurous Byzantine Chludov Psalter (9th century) has a small miniature showing the hand and dove above a Virgin & Child. The hand occasionally appears in Western "Annunciations", even as late as Simone Martini in the 14th century, by which time the dove, sometimes accompanied by a small image of God the Father, has become more common.
The hand appears at the top of a number of Late Antique apse mosaics in Rome and Ravenna, above a variety of compositions that feature either Christ or the cross, some covered by the regular contexts mentioned above, but others not. The motif is then repeated in much later mosaics from the 12th century.