414 REPORT — 186G. 



at that range ? Here we have, from equation (1), 



-g— =102 foot-tons, 



or 11-2 foot-tons per inch of the shot's circumference; and we also find 

 from the same equation that it requires 12-46 foot-tons per inch of the shot's 

 circumference to penetrate a 3-inch plate. 



The above shot therefore would not penetrate, although it would be very 

 near it. This result is borne out by roimds 986 and 993. 



Example VI. — Wo wish to test some steel shells of 115 lbs. weight and 6"92 

 inches diameter, fired from the 7-inch M L Woolwich gun, with 22 lbs. charge, 

 and a striking-velocitj'- at 200 yards of about 13S0 feet. We have a target, 

 cxjiressly constnicted for the trial of steel projectiles fired from heavy guns, 

 which consists of S-inch plates backed by about 20 inches of wood. Will 

 this suit oiu" purpose in the present instance ? 



ISTow, in order efi'ectuaUy to test a steel shell, the following conditions ought 

 to be fulfilled, viz. the iron plate which protects the target should not be of 

 greater thickness tlian that which the shell would be capable of penetrating 

 unbacked. Or, assuming that the shell, if fired blind would have as great a 

 penetration as a sliot of the same form and weight, the thickness of the plate 

 should be such as will admit of the shot getting its nose into the backing. 

 This condition is self-evident : for if we increase the thickness of the pro- 

 tecting plate beyond the power of the shot, it is manifest that the only result 

 of firing a shell at it woidd be an indent, and that it woidd not signify whether 

 there was powder in the shell or not. 



From equation (2), 



we can find the maximum thickness of plate which a shot of the same form 

 as the above sheR wUl penetrate. Substituting the values, we find 



6 = 7'09 inches. 



From this we see that a target faced with 8-inch plates is unsuitable for 

 testing shells from the 7-inch Woohvicli gun with the above charge, and, 

 moreover, that something less than 7 inches should be the maximum tliickness 

 of plate of a target placed for such a purpose at 200 yards. 



We could further demonstrate that the 8-inch target would do veiy well 

 for larger projectiles, such, for instance, as those fired from the 9-inch Wool- 

 wich gun of 12 tons. 



Example YII. — The wall piece is fired with a cylindrical steel shot of 

 0-34:4 lb. weight and 0-S7 inch diameter at a ^-inch plate, velocity on im- 

 pact being 1141 feet; ought it to penetrate it? and will it also penetrate a 

 1-inch plate ? 



Here we have 



and substituting the above values, we find 



6=0-906 inch. 



The shot woiild therefore penetrate a |-inch plate, but not one of 1 inch. 

 That this is correct we find from the Tables. 



Example VIII. — We wish to just penetrate a 5-5-iueh plate with a solid 

 steel hemispherical-headed shot of 6-88 inches diameter, fired from the 7-inch 



