PENETRATION OP IRON PLATES BY STEEL SHOT, 413 



Here we have from equation (2), 



and substituting the values above, we find 



5 = 6-486 inches. 



The thickness of plate to resist this shot ought therefore to be more than 

 6'5 inches. 



E.vample II. — The 68-pounder smooth-bore gun is fii-ed with a spherical 

 steel shot of 72-0 lbs. weight and 7-91 inches diameter, the striking-velocity 

 at 200 yards being 1365 feet; what thickness of unbacked plate will it 

 penetrate ? 



Here we have, as before, 



o = v\ / ; 



V 47r%^- 



and substituting the above values, 



h=5-2 inches. 



Round 906, fired with the above charge, failed to perforate a 5'5-inch plate, 

 although it indented it to a depth of 2-8 inches, and cracked off the plate 

 behind. We find, however, that the 68-poimder penetrated a 4-75-inch plate 

 on the " Small-plate" target (roiuid 842), and a 5-inch plate (round 960). 



Example III. — The 13-3-inch gun of 22 tons was fired at an 11-iuch plate 

 with a spherical steel shot of 344-4 lbs. weight and 13-24 inches diameter ; 

 charge 90 lbs., the striking-velocity being 1574 feet at 200 yards : ought it 

 to have penetrated the plate ? Now the thickness of unbacked plate which 

 this shot wUl penetrate can be found from equation (2), 



and substituting the above values, we find 



6 = 10-14 inches. 



Round 704, minute 11,287 shows that a shot of the above nature indented 

 an 11-inch unbacked plate to a depth of 4-9 inches and broke the plate in two. 



Example IV, — The embrasures of a fort are protected with unbacked wrought 

 iron plates of 8 inches thickness, with what velocity should a 250-lb. hemi- 

 spherical-headed rifie shot of 8-92 inches diameter strike so as to ensure pene- 

 tion ? Here we have, from equation (1), 



rRf/Z; 



and substituting the above values, we find 



v= 1197 feet. 



From this it follows that if the 9 -inch rifled Woolwich gim was fired with 

 its service-charge of 43 lbs, and a 250-lb. steel sliot it would penetrate an 

 unbacked 8-inch plate at about 1200 yards. 



Example V. — The 12-poimder B L Armstrong gun is fired with an elongated 

 steel shot of 12-60 lbs. weight and 2-90 inches diameter, charge 1-5 lb., velo- 

 city 10,807 feet at 200 yards * ; will this projectile penetrate a 3-inch plate 



* These Teloclties were all obsei-ved. 



