CHAPTER IX. Machine-guns. The Hotchkiss Revolving Cannon. The Gatling Gun. The Gardner Gun. The Maxim Gun. The Metallic Carriage for Machine-guns. HOTCHKISS REVOLVING CANNON. [Illustration: FIG. 82.] There are two sizes for field-artillery, viz.: light and heavy, both having the same caliber. DESCRIPTION. Light. Heavy. Calibre inches 1.45 1.45 Length of gun " 46.4 70.4 Height of trunnions above tread " 35 42.4 Length of gun-barrel " 29.1 50.1 Number of barrels 5 5 Weight of each barrel pounds 30.8 79 Length of rifled bore inches 24.7 43.4 Number of lands 12 12 Pitch of rifling degrees 6 6 Weight of gun complete pounds 495 1045 The gun consists of five main parts: the group of barrels, the breech-piece, the mechanism, the frame, and the attachments. THE GROUP OF BARRELS. The five barrels are assembled around a main shaft by being secured in two bronze assembling-disks. Both disks are bolted to the main shaft, so that barrels, disks, and shaft revolve together. The main shaft goes into the breech-piece, and has screwed and bolted to its end a heavy steel pin-wheel, which connects the barrel-system with the mechanism. [Illustration: FIG. 83. _Hotchkiss R. C. Rotating Device._ _LEGEND_ _C. Crank Shaft._ _L. Loading Piston._ _P. 5, Pinions._ _T. Trap Door._ _W. Worm._ ] THE BREECH-PIECE. This is a cast-iron block, the front half solid and pierced with the channels necessary for feeding, loading, firing, and extracting ammunition, and the rear half hollow to form a chamber for the mechanism, with guideways and journals for its movement and support. In the upper front face a channelway is cut from the loading-hole around almost to the firing-point, the bottom being inclined so that as the cartridge moves along it during the revolution of the barrels it is pushed forward and close home.