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Nov. 9, 1882 | 
NATURE 
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It was in this way that his gun made in 1860 was con- 
structed, and we believe the same principle has been 
adopted by Capt. Schultz in the wire guns built under his 
directions by the French Government. Thus the circum- 
ferential strain is provided for by one portion of material, 
and the longitudinal strain by another, and it does not 
admit of a doubt that this is far preferable to subjecting 
the same material to two strains at right angles to each 
other at one and the same time. 
Another objection has been taken to wire guns, and it 
is this. It is well known that guns become heated by 
firing, and it is thought that this heating would disturb 
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the tensions to such an extent as to_render all the calcu- 
lations of strain useless. Now if this be an objection, it 
applies with far greater force to the system of hoop con- 
struction than to that of wire, but as there is much mis- 
conception on this point it is desirable to say a few words 
about it. 
In the first place, it is a mistake to suppose that the 
heating ot guns depends chiefly on the heat absorbed by 
the metal from the powder gases. Though this heat is 
very intense, its application is for a very small fraction of 
a second, and it may be shown that in this very short 
time only a small amount of heat can be absorbed by 
the surface of the gun exposed to it. It may further 
be shown, that during the very short time the heat is 
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applied, it can only be transmitted by internal conduction 
to a very small depth into the metal of the gun. But as 
guns do heat by firing, how is this to be accounted for ? 
The reason seems to be the following. By the explosion 
of the powder, a considerable amount of mechanical 
energy is absorbed in expanding the gun against the 
elastic form of the material. When the projectile leaves 
the gun, the internal pressure is removed, the mechanical 
energy is thus given back, but as it does no external work, 
it appears in the form of heat, which remains in the metal 
of the gun, until it is dissipated by convection through the 
surrounding air. 
We are-quite aware that this explanation does mot 
agree with the views of some physicists of great reputa- 
