The principal breech-loading arms in use in the Union armies were the Sharps and the Spencer. In the Sharps carbine the barrel was closed by a sliding breech-piece which moved at right angles with the axis of the piece, the breech being opened and closed by pulling down and raising up the trigger-guard. The Spencer carbine was a magazine rifle, and was greatly superior to the Sharps. The magazine of the rifle lay in the butt of the stock, and was capable of holding seven cartridges. As the cartridge was fired and ejected another was pushed forward into the breech by a spiral spring in the butt of the piece. The Spencer carbine used metallic cartridges. The introduction of these cartridges was one of the most remarkable advances in the art of war made during the present century. The cartridge in use in 1864–65 is shown in the accompanying figure; it consisted of a thin copper case firmly attached to the bullet containing the powder, and having at its base a small metallic anvil, in a cavity of which was placed the fulminate, which was exploded by means of a firing pin, driven in by a blow of the hammer. The advantages of the metallic cartridge can scarcely be overestimated; it rendered obsolete the percussion cap, and being water-proof it did away with the ever-present bugbear of damp ammunition. The old injunction, “Put your trust in God and keep your powder dry,” has consequently lost much of its force; for while it is to be hoped that the soldier will continue to place his reliance upon Providence, the latter part of the advice can now be safely ignored. [Illustration: METALLIC CARTRIDGE OF 1864–65.] Among the many advantages possessed by the breech-loader over the muzzle-loader, the principal ones are greater rapidity of fire, ease of loading in any position, diminished danger of accidents in loading, and the impossibility of putting more than one charge in the piece at the same time. This last advantage is by no means slight. Among 27,000 muzzle-loading muskets picked up on the battlefield of Gettysburg, at least 24,000 were loaded. Of these about half contained two charges, one fourth held from three to ten charges, and one musket contained twenty-three cartridges.