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POPULAR SCIENCE REVIEW. 
induces them to pay more attention to the dynamic resistance of materials. 
It will lead to the explanation of many catastrophes (boiler explosions 
and the fracture of the Hartley Colliery beam, for example) which have 
been considered almost inexplicable. And war will thus have nourished 
the arts anew, and yielded fruits of peace. 
Mr. Fairbairn shows that the destructive power of the shot depends on 
its vis viva, or the work accumulated in it during the explosion of the 
powder, and which is known to vary as the product of the weight of the 
shot and the square of the velocity generated. This product is in turn 
known to vary as the weight of powder in the charge. The shot is, 
therefore, merely a carrier of the energy disengaged by the chemical decom- 
position of the powder. That the destructive power of the shot increases 
with the square of the velocity explains the inefficiency of the American 
200-pounder “ Parrot guns,” in which only small charges of powder 
can be expended as compared with the guns employed in the experi- 
ments in this country. It also explains the enormous power of the 
800-pounder smooth-bore at Slioehuryness when firing a 150-pounder ball 
with a charge of 50 lb. of powder. Of this last Mr. Fairbairn says : — 
“We had just arrived at the desired point of security when the thun- 
dering 300-pounder, smooth bore, upset our calculations and levelled the 
whole fabric with the ground.” 
The velocity of the 150 lb. shot probably approached 2,000 feet per 
second. 
On the vexed subject of “ships versus forts” Mr. Fairbairn sides with 
Lord Palmerston. He says : — 
“ A great outcry has been raised about the inutility of forts ; and the 
Government, in compliance with the general wish, has suspended those at 
Spithead ; I think improperly so, as the recent experiments clearly 
demonstrate that no vessel, however well protected by armour-plates, 
could resist the effects of such powerful artillery ” (as the 800-pounder 
alluded to above). 
Whether the doubt, expressed in the last paragraph, as to the possibility 
of obtaining invulnerability in ships is well founded must be determined 
by further experiments ; but, looking to the law enunciated by Mr. Fair- 
bairn, that the resistance of plates increases as the square of the thickness, 
it would appear that at present our means of defence in ships are in 
advance of the artillery which can be brought to bear against them. The 
enormous 800-pounder only just penetrated the target representing a 
section of the Warrior and protected by 4^-inch plates, and that, too, 
after it had been struck by 8,229 lb. weight of metal. But 5 and 5b inch 
plates are being employed, which will increase the resisting power by 
25 and 50 per cent, respectively, and it is doubtful whether these would 
be penetrated by even the most powerful modern artillery, at least with 
the present cast-iron service-shot. In America, 30A-inch plates have been 
used, but there is, no doubt, a limit to the thickness to which the law of 
the squares applies. Very thick plates of wrought-iron have been found to 
break brittle like plates of steel, either from a deterioration in the 
quality of the material or from the rigidity of a thick mass, causing 
fracture according to a different law. The entire invulnerability of the 
