One summer afternoon the experiments took place in a shady grove in the Charterhouse garden. Screens--“of finest tissue paper”--were set up at intervals of fifty feet, and a common musket bored for an ounce ball was firmly fixed in a vice so as to fire through the screens. By repeated discharges the various deflections from the original plane of departure were clearly shown; some of the balls whirled to the right, some to the left of the vertical plane in which the musket lay. But not only was the fact of this deflection established to the satisfaction of the visitors. A simple but dramatic proof was afforded them of the correctness of Robins’ surmise that the cause was the whirling of the ball in flight. A musket-barrel was bent so that its last three or four inches pointed to the left of the original plane of flight. The ball when fired would then be expected to be thrown to the left of the original plane. But, said Robins, since in passing through the bent part the ball would be forced to roll upon the right-hand side of the barrel; and as thereby the left side of the ball would turn up against the air, and would increase the resistance on that side; then, notwithstanding the bend of the piece to the left, the bullet itself might incurvate towards the right. “And this, upon trial, did most remarkably happen.”[83] Robins by now had gained a European reputation. Mathematical controversy and experiments in gunnery continued to occupy his time and absorb his energies, and it was not long before he was again at the rostrum of the Royal Society, uttering his eloquent prediction as to the future of rifled guns. Speaking with all the emphasis at his command he urged on his hearers the importance of applying rifling not only to fire-arms but to heavy ordnance. That State, he said, which first comprehended the advantages of rifled pieces; which first facilitated their construction and armed its armies with them; would by them acquire a superiority which would perhaps fall little short of the wonderful effects formerly produced by the first appearance of fire-arms. His words had little or no effect. Mechanical science was not then equal to the task. A whole century was to elapse before rifled ordnance came into general use. The genius of Whitworth was required to enable the workshops of the world to cope with its refined construction. Another subject which attracted Robins’ attention at this time was fortification, the sister art of gunnery, which now had a vogue as a result of the great continental wars. He was evidently regarded as an authority on the subject, for we find him, in 1747, invited by the Prince of Orange to assist in the defence of Berghen-op-Zoom, then invested and shortly afterwards taken by the French.