Young temperament
"Young temperament" may refer to either of a pair of well temperaments described by Thomas Young in a letter dated July 9, 1799, to the Royal Society of London. The letter was read at the Society's meeting of January 16, 1800, and included in its Philosophical Transactions for that year. The temperaments are referred to individually as "Young's first temperament" and "Young's second temperament", more briefly as "Young's No. 1" and "Young's No. 2", or with some other variations of these expressions.
Young argued that there were good reasons for choosing a temperament to make "the harmony most perfect in those keys which are the most frequently used", and presented his first temperament as a way of achieving this. He gave his second temperament as a method of "very simply" producing "nearly the same effect".
In his first temperament, Young chose to make the major third C-E wider than just by 1⁄4 of a syntonic comma (about 5 cents, 
Play ), and the major third F♯-A♯ (B♭) wider than just by a full syntonic comma (about 22 cents, Play ). He achieved the first by making each of the fifths C-G, G-D, D-A and A-E narrower than just by 3⁄16 of a syntonic comma, and the second by making each of the fifths F♯-C♯, C♯-G♯, G♯-D♯ (E♭) and E♭-B♭ perfectly just. The remaining fifths, E-B, B-F♯, B♭-F and F-C were all made the same size, chosen so that the circle of fifths would close—that is, so that the total span of all twelve fifths would be exactly seven octaves. The resulting fifths are narrower than just by about 1⁄12 of a syntonic comma, or 1.8 cents, and differ from an equal temperament fifth by only about 1⁄8 of a cent. The exact and approximate numerical sizes of the three types of fifth, in cents, are as follows:
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