[26]Clavis 1694, p. 19, and the Clavis of 1631, p. 8.
[27]See for instance, Oughtred’s Elementi decimi Euclidis declaratio, 1652, p. 1, where he uses A and E, and also a and e.
[28]See Christophori Clavii Bambergensis Operum mathematicorum, tomus secundus, Moguntiae, M.DC.XI, algebra, p. 39.
[29]Christophori Clavii operum mathematicorum Tomus Secundus, Moguntiae, M.DC.XI, Epitome arithmeticae, p. 36.
[30]See F. Cajori, “The Cross × as a Symbol of Multiplication,” in Nature, Vol. XCIV (1914), p. 363.
[31]See Elementi decimi Euclidis declaratio, 1652, p. 2.
[32]See Johannis Wallisii Operum mathematicorum pars prima, Oxonii, 1657, p. 247.
[33]Clavis of 1631, chap. xix, sec. 5, p. 50.
[34]We have noticed the representation of known quantities by consonants and the unknown by vowels in Wingate’s Arithmetick made easie, edited by John Kersey, London, 1650, algebra, p. 382; and in the second part, section 19, of Jonas Moore’s Arithmetick in two parts, London, 1660, Moore suggests as an alternative the use of z, y, x, etc., for the unknowns. The practice of representing unknowns by vowels did not spread widely in England.
[35]Philosophical Transactions, Vol. XIX, No. 231, London, p. 652.