Various, Philosophical transactions, Vol… (1759)
“ If, therefore, that fluxion be denoted by ̇υ, we shall have flux. Q ́ q + R ́ r &c. = ̇υ, and consequently Q ́ q + R ́ r &c. = υ. But Q ́ q + R ́ r &c. (by the same notation) appears to be the fluxion of Q ́q ́ + R ́r ́ &c. (or of Qq + Rr &c.) arising by substituting u for ẏ, making u alone variable, and casting off ̇u. Whence the followingGeneral Rule. Take the fluxion of the given expression (whose fluent is required to be a maximum or minimum) making ẏ alone variable ”
