464 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



striking of the shell. The fuse is generally made to burn about 

 20 seconds, and when the shell is to be fired, it is shortened to 

 the required length. The percussion shell has ben publicly* 

 known for six or eight years, but as usually constructed has seve- 

 ral disadvantages. It has a percussion cap upon its front and is 

 fired by the striking of the shell. One disadvantage attends this 

 arrangement, namely, the danger of premature explosion, from 

 dropping or careless usage. Of course it could not be safely 

 rammed down. It has been attempted to construct the percus- 

 sion cap of such a material that it would stand an ordinary blow. 

 One form of the Hotchkiss' shell, is so constructed that the per- 

 cussion cap is enclosed within the ball. For this purpose there 

 is a little chamber within which is a sliding tube, and upon the 

 front of this tube the percussion cap is placed. When the cannon 

 is fired, the tube having been brought back by its inertier, the 

 moment the shell strikes any object, or even against the water, 

 the tube flies forward and strikes the front end of its chamber 

 with sulficient force to ignite it. Yet the cap is protected from 

 any blow, and the mere dropping of the shell cannot ignite it. 

 But this plan is attended with another difficulty. It has been 

 found that the shells thus arranged, are liable to explode imme- 

 diately upon emerging from the guii. If you can get them safely 

 past that point they will fly until they strike. The explosion at 

 this period of the flight has been ascribed to the resistance of the 

 air ; but I think I see another cause for it which is more likely to 

 be the true one. 



Mr. Sykes. — Is it not the elasticity of the metal ? The tubes 

 come back until they strike, and then rebound with such force as 

 to strike the front end, and the cap is fired. 



Mr. Stetson. — That is exactly what I suppose to be the cause ; 

 and Mr. Hotchkiss has successfully guarded against that difficulty 

 by putting a soft and inelastic material, such as lead or soft 

 putty, at the back to prevent this rebound. It is worthy of 

 remark that the percussion shell, although fired by the striking 

 of the shell, yet penetrates the whole depth due to the force of 

 its impact before the explosion takes place ; so that in firing 

 against ships the explosion does not take place until after it has 

 passed through the first wall of the vessel. 



•Experiments were made by Robert L. Stevens in August 1817, in the presence of 

 President Monroe. The results were not made public. — J. R. 



