Let us endeavour, first, to understand something of the movement of gun-shots in their simplest form. A gun-barrel, consisting of a bar of metal thicker at one end (where it has to withstand the first shock of the gunpowder) than at the other, is bored out throughout its length into a smooth hollow cylinder; this cylinder is closed at one end by the breech, which has a small opening in it, through which the charge is ignited. A charge of powder is placed in the closed end, and on the top of this the ball, say, a spherical one, such as our ancestors in their simplicity considered the best. The powder being ignited, rapidly, though not instantaneously, becomes converted into gas, and the _permanent_ gases generated will, at the temperature estimated to be produced by the combustion (3,000° Fahr.), occupy a volume under the pressure of the atmosphere alone of over 2,000 times that of the bulk of the powder. This point, as well as the elasticity of the gases, both of the permanent ones and of the vapour of water or steam from the moisture in the powder, has never been accurately determined,[15] and various estimates have been formed; but if we take Dr. Hutton’s—a rather low one, viz.—that the first force of fired gunpowder was equal to 2,000 atmospheres (30,000 lbs. on the square inch), and that, as Mr. Robins computed, the velocity of expansion was about 7,000 feet per second, we shall have some idea of the enormous force which is exerted in the direction of the bullet to move it, of the breech of the gun to make it kick, and of the sides of the barrel to burst it. Notwithstanding Mr. Robins’ advice, we certainly never, till very lately, made the most of the power of committing homicide supplied by this powerful agent; but we used it in the most wasteful and vicious manner. All improvements—and many were suggested at different times to remedy defects, which he principally pointed out, like the inventions of printing and of gunpowder itself—lay fallow for long before they were taken up. They were premature. If our fathers had killed men clumsily, why should we not do the same? No one cared much, except the professionals, whether it required 100 or 1,000 bullets, on an average, to kill a man at 100 yards’ distance. Now we take more interest in such amusements; every one’s attention is turned to the best means of thinning his fellow-creatures; and we are not at all content with the glorious uncertainty which formerly prevailed when every bullet found its own billet: we like to kill our particular man, not his next neighbour, or one thirty yards off. In order to see why we are so much more certain with our Whitworth, or Enfield, or Armstrong, of hitting the man we aim at, let us first examine how a bullet flies; and then by understanding how (badly) our fathers applied the force we have described to make it fly, we shall be able to appreciate how well we do it ourselves.