It is to be noted that it was only in increased accuracy of flight that the rifled gun had a superiority over the smooth-bore; no increase in ranging power was possessed by it. And yet this claim is constantly made by old writers, that, probably (as they say) owing to the fact that increased resistance of the ball to initial motion gave time for all the charge to be thoroughly ignited, the rifled gun carried further than the smooth-bore. As a fact, the contrary was true; other things being equal, the range of the rifle was actually less than that of the smooth-bore. The explanation of the paradox was given by Robins. “It is not surprising,” he said, “that those habituated to the use of rifled pieces gave way to prepossessions like these; for they found that with them they could fire at a mark with tolerable success, though it were placed at three or four times the distance to which the ordinary pieces were supposed to reach: and therefore as they were ignorant of the true cause of this variation ... it was not unnatural for them to imagine, that the superiority in the effect of rifled pieces was owing either to a more violent impulse at first, or to a more easy passage through the air.” The true value of the spiral grooving resided, of course, in the spinning motion which it gave the ball. By making this spin uniform two variable factors determining the trajectory were thereby transformed into constants: first, the effect just mentioned, the influence of the varying resistance of the air on the parts of the ball which met it at different speeds, some parts moving forward relatively to its centre and some parts retreating; secondly, the effect of eccentricity of mass and irregularity of exterior surface, which were both almost nullified by the rotation. The importance of this second effect may not at first sight be apparent. It must be remembered, however, that the balls used in those days were of the roughest description; cast in hand moulds, “drawn” in cooling to such an extent that in a large proportion an actual cavity was left in their interior, which could be revealed only by cutting them open; their burrs removed with pincers, their surface rough and broken, their shape distorted by the ramrod’s blows.