involved in the Construction of Artillery. 17.5 



in which c is the weight of the powder, and tv' that of the shot, a a coefficient, 

 having the following values for different windages: — 



shows that its value only varies from 5-0 to 3-2 for the extreme range of windage 

 from minimum to maximum ; so neither can the increase of strain on the gun 

 due merely to diminished windage be the true cause of frequent bursting in 

 firing heated shot. 



9. — Nature and Effects of Local Expansion by Heat on Guns. 



77. What, then, is the cause ? I conceive it may be proved to be the enor- 

 mous strain produced locally upon the exterior portions of the metal of the gun in the 

 neighbourhood of the charge., by the expansion of the interior of the chase or bore due 

 to the rapid communication of heat from the shot suddenly lodged within the gun 

 bringing its external circumference at the place into a violent state of tension, 

 in which state the gun is directly exposed to the further, suddenly applied and 

 jarring sti'ain of the discharge. 



78. The diagram may represent in longitudinal and in transverse section a 

 portion of the bore of a gun with a red-hot shot lodged within it preparatory 



2 A 2 



