408 



KKi-ORT I86(i, 



If we examine Table III., it appears that penetration* varies nearly in the 

 inverse ratio of the diameter. The only round which does not bear this out 

 is No. 1009 ; and in this ease the fault may have been in the steel of which 

 the projectile was composed. Thus Nos. 1008 and 765 agree exactly ; 1011 

 and 1026 are practically equal in effect, and IS'os. 1027, 1012, and 1013 are 

 all very similar in their efi'ccts. As before mentioned, in an experiment of 

 such a practical description we must not look for too much theoretical harmony 

 in the results ; and when wc remember that steel and iron vary so much in 

 quality, exact results cannot be expected. 



The Committee, however, determined to repeat tlie experiments against 

 4-5-inch plates, and to fire with such charges that the projectiles should strike 

 with a force which would be merely suiRcient to Just penetrate throiigh tlie 

 plate t. 



It appears from Table II., round 1008, that a G-22 inch projectile is Jast 

 able to penetrate a 5-5-inch plate, Avith a "work" on impact of about 825 

 foot-tons ; and if we assume that the resistance of the plate varies as the 

 square of its thickness, we shall have the following proportion to determine 

 the " work " necessary to penetrate a 4-5-inch plate with the same projec- 

 tile, viz. : — 



5-5= : 825 : : 4-5^ : x ; 

 and .r=552 foot-tons. 



In order therefore to Just penetrate a 4-5-inch wrought iron unbacked 

 plate, a 6-22-inch solid steel hemispherical-headed shot ought to strike with 

 a " work " represented by about 552 foot-tons ; and if wc take the weights 

 of the projectiles to be approximately 



35-56 



03-87 



71-00 



106-62 



the following Table gives the velocities which each of these projectiles must be 

 moving at, in order that the " work " on impact may equal 552 foot-tons. 



Table IV, — Showing the weights of hemispherical-headed steel 6-22-inch 

 shot, with the velocity necessary to give a constant " work"' of 552 foot- 

 tons at 100 yards. 



lbs. 



Having carried the investigation thus far, it became necessary to determine 

 whether the assumption, that the resistance of wrought-iron plates varies 

 as the square of their thickness, was correct, — in other words, to ascertain 

 whether a " work '' of 552 foot-tons would ji'st penetrate a 4-5-inch plate 



* See note +, p. 403. 



t The results obtuinecl by the previous esperhiieiit bad proved that the " work " in some 

 of the shot was more than sufRcient to cilect complete perforation; mid the aim of the 

 second experiment, against -I'o-inch plates, was to so apportion the charges that the several 

 projectiles should be or)]y Just capable of getting through the plate. 



