MECHANICS AND USEFUL ARTS. 43 



The breech, which has now to be added, is composed of several iron slabs, 

 something like the staves of a barrel, which are bent into a cylindrical form, 

 and welded at the edges, when red-hot, under the steam-hammer. In the 

 breech, the fibre of the metal runs in the direction of the length of the gun, 

 while in the other parts it winds round and round trans versely. This is 

 done to give greater strength to the breech in sustaining the whole back- 

 ward thrust of the explosion. The breech thus formed is "shrunk on" to 

 the rest of the gun; and to add still more to its strength, two double coils of 

 wrought iron are rolled on with the fibre at right angles to that of the 

 breech underneath. The piece now exhibits very much the appearance of 

 what is called a three-draw telescope the tube, the trunnion-piece, and 

 the breech representing the three " draws" of the glass when pulled out. 



So much for the rough work of the gun; AVC now come to the finer and 

 more delicate process. Having been pared clown on the outside to its proper 

 size, the gun passes to the measurers, who, with an instrument called a 

 micrometer, measure each part with mathematical accuracy. The slightest 

 deviation of any portion from its exact size, even to the fraction of a hair's 

 breadth, is rigidly pointed out, and has to be amended. The boring and 

 rifling of the piece are next performed, in a large, tidy, well-lighted room, 

 where there is no noise, or smoke, or confusion, as in the forging shop. 

 The gun is placed erect in the boring-machine, and revolves gently round 

 the big gimlet, which slowly but surely wends its way downwards, scooping 

 out the superfluous metal from the interior of the tube. 



Four pieces can be bored at once by each machine. This is the lengthiest 

 process the gun lias to go through. It has to be performed twice, each time 

 occupying six hours. First, the gun is bored to within a -j-oV <y of an inch 

 in its proper diameter; and the second time it is finished. The rifling is 

 performed in a turning-lathe, and occupies some five hours. There are 

 thirty-eight fine, sharp grooves, of a peculiar angular shape "with the 

 driving side angular," in the words of the inventor, " and the opposite side 

 rounded;" and the turn of the rifling is very slight. 



Where the touch-hole of an ordinary gun would be, a square hole is cut 

 for the introduction of the vent-piece, or stopper, which, with the breech- 

 screw, completes the gun. The stopper is a circular piece of steel, faced 

 with copper, which fits into the end of the rifled barrel with the most exact 

 nicety. Upon this little piece of metal depends, in a great measure, the 

 efficiency of the gun ; because, unless it hermetically closed the cavity, a 

 portion of the explosive force would escape, and the discharge would be 

 weakened. The copper facing of the stopper is prepared with great care. 

 It has to be sharpened with a file after so many rounds, and a duplicate 

 accompanies every gun. The touch-hole runs through the vent-piece down 

 into the chamber of the gun. The breech of the gun receives a powerful 

 hollow screw, which presses against the vent-piece, and is easily tightened or 

 loosened by means of a common weighted handle. When the stopper is 

 out, the gun is a hollow tube from end to end. Chambei-s's Journal. 



PRACTICAL EFFECTS OF THE ARMSTRONG GUN. 



The following is a description of the practical effects of the Armstrong 

 gun, as displayed in recent experiments in England, the target selected 

 being a Martello tower on the channel coast : The guns employed were a 

 forty-pounder of thirty-one cwt., an eighty -pounder of sixty-three cwt., and 



