For thoughtful men of all ages, as we have already noted, the flight of bodies through air had had an absorbing interest. The subject was one of perennial disputation. The vagaries of projectiles, the laws governing the discharge of balls from cannon, could not fail to arouse the curiosity of an enthusiast like Robins, and he now set himself in earnest to discover them by an examination of existing data, by pure reason, and by actual experiment. Perusal of such books as had been written on the subject soon convinced him of the shallowness of existing theories. Of the English authors scarcely any two agreed with one another, and all of them carped at Tartaglia, the Italian scientist who in the classic book of the sixteenth century tried to uphold Galileo’s theory of parabolic motion as applied to military projectiles. But what struck Robins most forcibly about all their writings was the almost entire absence of trial and experiment by which to confirm their dogmatical assertions. This absence of any appeal to experiment was certainly not confined to treatises on gunnery; it was a conspicuous feature of most of the classical attempts to advance the knowledge of physical science. Yet the flight of projectiles was a problem which lent itself with ease to that inductive method of discovering its laws through a careful accumulation of facts. This work had not been done. Of all the native writers upon gunnery only four had ventured out of two dimensions; only four had troubled to measure definite ranges. All four asserted the general proposition that the motion of bodies was parabolic. Only one noticed that practice did not support this theory, and he, with misapplied ingenuity, called in aid the traditional hypothesis of a violent, a crooked, and a natural motion. Which wrong hypothesis enabled him, since he could choose for himself the point at which the straight motion ceased, to square all his results with his precious theory.