PENETRATION OF IRON PLATES BY STEEL SHOT. 421 



On tlie Penetration into UnbacJced Plates. 



"We have hitherto considered the effects due to absohite penetration or 

 j)erforation, that is, when a clean hole is made through the iron plate. Let 

 us now examine the results of various experiments where the effect was to 

 bend and indent the plate in consequence of the force not being sufBcient to 

 perforate it. 



The Tables in the Appendix give the results of various experiments at un- 

 backed plates. 



From these Tables it appears that, when the shot is unable to perforate, the 

 effects are very variable and difficult to compute. 



Thus the total effect or " work done " by round 986 was made up of the 

 following items : — 



1st. Indent 2-3 inches. 



2nd. " "Work " expended in cracking indent. 



3rd. " "Work " in cracking and bulging rear of jilatc. 



4th. " "Work " in cracking the head of, and " setting up " the shot from 7*4 

 inches to 6-74 inches. 



Again, we have, round 993, fired under the same circumstances : — 



1st. Indent 2-2 inches. 



2nd. " "Work " expended in twisting the shot, cracking its head, and 

 reducing its length from 7'4 to 6-.5 inches. 



Here no " work " was expended in cracking the indent or the back of the 

 plate, but, on the other hand, the shot was more distorted in form, and more 

 reduced in length. 



It would be difficult to reduce such results to any law, unless we were pos- 

 sessed of data furnished by a number of carefully conducted experiments 

 made with shot of the same form and quality, and plates of equal strength. 



It is submitted, however, that the knowledge of how far a shot will penetrate 

 into an iron plate is of little practical value. '^Ve can determine with a close 

 degree of ajiproximation whether it will penetrate throu[/Ji the plate or not ; 

 and that is the chief point. It is, however, interesting to observe the differ- 

 ence between the way in which the work is done in the two cases, viz. when 

 the plate can be perforated, and when it cannot. 



Thus round 986, with a luorl- of about 102 foot-tons, only penetrated to a 

 depth of 2-3 inches in a 3-inch plate, whereas it would have perforated the 

 plate if the ivorJc had been ] 14 foot-tons. 



The 68-pounder smooth-bore, firing solid steel si^herical shot with 16-lb. 

 charges, could perforate a 5-inch plate, but would only penetrate to a depth of 

 about 3 inches in a 5^ -inch plate. 



The effects of the wall-piece, firing steel flat-headed shot, are very strange. 

 Thus this projectile can penetrate, at 25 yards, all plates up to and including 

 |-inch; it fails to penetrate an inch plate, and indents it 0-28 inch, but it 

 indents a 5-inch plate almost as much ; and there is no difference whatever 

 between the indent in a 5- and a 4-inch plate. This seems to prove that 

 anything above a 4-inch plate may be regarded as being of infinite thickness, 

 relatively, to a wall-piece projectile. 



Examination of tlie Pesults of various Experiments aijainst Tanjets rejpre- 



seniinf) Iron-clad Vessels. 



The experiments before detailed have indicated that the comparative effect 

 produced on iron defences by steel shot can be very closely represented by 

 the vis viva of the projectUe on impact — and that it is of little importance 



