MECHANICS AND USEFUL ARTS. 113 



The accelerator plugs may be made of soft cast steel fitting 

 closely in and protecting the cast iron from the fire of the powder. 

 Instead of these steel chambers, ordinary plugs, only half the 

 diameter of the powder chambers, have heretofore been used, but 

 though no cast-iron accelerating chamber has ever failed, it is be- 

 lieved that a protection of half an inch of soft steel, which will 

 keep the fire out of any defect that may exist in the cast iron, will 

 increase its durability. 



When the gun is fired the shot is driven by the initial charge 

 past the first accelerator, when the fire sets back down into and 

 lights the mammoth powder in this accelerator. This raises the 

 pressure perhaps nearly as high as it was raised by the small 

 initial charge before the inertia of the shot was overcome. The 

 action of each of the remaining accelerators is the same. It is 

 found by experiment that every additional accelerator increases 

 the force of the shot, and ever} 7 addition to the charge in the last 

 accelerator seems to increase the force of the shot as much as 

 though it was added to the first accelerator or to the charge in the 

 breech. 



Though this breech-loading arrangement is somewhat similar to 

 that of Mr. Whitworth's cannon, it is believed to be a much safer 

 arrangement for the following reasons : 



1st. When the gun is fired there is no pressure in the barrel 

 within 6 inches of the end of the tube, and that 6 inches acts as a 

 band to strengthen the tube. 



2d. As we use not over one-quarter as much powder in the 

 breech, the pressure of the fire acts against not over one-quarter 

 as much of the length of the bore of the gun before the shot 

 starts. 



3d. The sabot in this accelerator prevents the fire of the powder 

 from pressing around the shot, and the back 9 inches of the shot is 

 freed on its bearings, so that the strain from rotating the shot falls 

 entirely on the bearings in front. The part of the gun that is 

 strained by the pressure of the fire is thus separated a considerable 

 distance from the part that is strained in rotating the shot. This 

 separation of these two strains by 9 inches of metal on which there 

 is no strain greatly lessens the danger of bursting the gun, and re- 

 moves the objection to the wedge action of the Whitworth shot, or 

 any other shot that centres in the gun, as well as the objections to 

 the large class of shot that are rotated by the sabot, or by a ring 

 of softer metal. 



The following table gives the comparative ranges of cannon, as 

 compiled from official sources : 



Diameter , Elevation. s 



of bore. 2. 5. 10. 



Inches. Yards. Yards. Yards. 



Old 12-poundcr, round ball, . . 909 1,663 .... 

 Old 42-pounder, round ball, . . 1,010 1,995 .... 

 Rodman's 400-pounder in use on moni- 

 tors, with 40 Ibs. good powder, 15 812 1,518 2,425 

 Parrott's 10-pounder, 2.9 930 2,000 3,200 

 Parrott's 2'J-pounder, 3.64 950 2,100 3,350 

 rarrott's 30-pounder, 4.2 1,000 2,200 3,500 



10* 



