Galileo explored on several folio pages of Ms. Gal. 72 'what happens when a body is urged by a motion compounded of one which is horizontal and uniform and of another which is vertical but naturally accelerated; from these two components results the path of a projectile, which is a parabola. The problem is to determine the speed [impeto] of the projectile at each point.' (*Discorsi*, before Proposition 3, Theorem 3 of Book 3 of *De motu locali*) He considered, in particular, a composition rule according to which the horizontal impetus is just added to the vertical one like a number and later found the composition rule as formulated in 3/04-pr-01, according to which the square of the compounded impetus is equal to the sum of the squares of the components. (See alsoDamerow et al. 1992. |