Prof. Treadweli’s Improvements in Cannon. 101 
than that of any layer nearer the axis. And if the walls of the 
cylinder are thick, and the internal pressure surpasses the tensile 
strength of the material, its inner layer will break before the 
outer one has been notably strained. Hence the tensile strength 
of a square inch bar of the material is the measure of the maxi- 
consideration. The improvement does away with this limit, and 
enables us to go indefinitely beyond it. : 
his is accomplished by so constructing the gun that the inner 
layers are compressed by the outer; whereby the internal pres- 
sure is first resisted by the outer layers, which must be distended 
enough to allow the internal compressed portion to attain its 
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