And that is a view which, it is suggested, might be expanded to give a motive or combination of motives which may well have operated to induce the early gunmakers to cut grooves in their musket-barrels. Thus: the variations in the flight of spherical lead balls fired from smooth-bore guns were chiefly due (though these causes were not clearly appreciated till a much later date) to the incalculable effect of windage and to the varying axis about which spin took place. If by any means windage could be reduced, and if the ball could be made to assume a central position in the bore and spin about a definite axis in its flight, a large increase in accuracy would be attained. Suppose, for instance, a single groove or gutter were filed along the barrel parallel with its axis. The effect surely would be, by creating a rush of powder-gases along this groove, to cause the ball, under the tangential impulse of the gases, to rotate always in the same plane as it passed through the bore. And thus by the cutting of this single groove a uniformity of flight of the ball would be attained which was unattainable without the groove. The same effect, in fact, was produced by Robins when he bent the musket barrel. He demonstrated that the result was to make the ball roll on a definite part of the barrel and thus to deviate during flight in a definite direction. He might have shewn, as another result of his experiment, that by giving the ball a uniform spin he had endowed it with a regularity of flight, or accuracy, many times greater than it before possessed. Or suppose that, instead of one groove, two or more grooves were filed in the same way. While the above advantage derived from the single groove would be less fully obtained, another would result. By providing a space on each side into which fouling might spread, and into which the plastic metal of the ball might be intruded by the pressure of the ramrod, their presence would certainly allow of a tight-fitting ball being used. The loss in efficiency of discharge due to friction between ball and barrel would be more than compensated for by the annihilation of windage.[114] Suppose, however, that the grooves were augmented in number until they became a series of triangular serrations all round the interior of the barrel. The value of this formation might lie, not so much in the grooves, as in the ends or points of the serrations which supported the ball and held it in a central position on the true axis of the gun. In short, the prime idea of the gunmaker may have been, not so much the provision of grooves, as the provision of internal ribs for holding the ball truly in the musket. Whatever the cause or motive which led to its adoption, the rifling of musket barrels became a common practice in the sixteenth century. Two significant quotations will suffice to show the period of the invention. The first is an edict issued by the Swiss Government in 1563: