174 



Mr. Mallet on the Physical Conditions 



probably with advantage be either cast in sand (like shells), or, if in iron moulds, 

 afterwards annealed. The use of iron moulds, however, appears to be aban- 

 doned in several British foundries. 



74. Shot frequently heated red-hot are said permanently to enlarge ; this 

 needs confirmation, but it would follow as a consequence of the conditions 

 assumed above to account for Sir 11. Douglas's figures. The explanation, 

 therefore, would receive some corroboration from this, if established. 



75. We may, however, assume the mean diametric expansion of white-hot 

 shot (a temperature never reached in practice) as about -^ the diameter ; and the 

 following Table will show the impossibility of shot of the six largest classes of 

 ordnance becoming jammed in the gun from this cause, even assuming a certain 

 amount of internal expansion in the gun itself, which, if it produce diminution 

 of bore at all (as we shall hereafter see reason to doubt), must do so imper- 

 ceptibly, from the slight degree of heat communicated, and from its effect being 

 divided between compression of the interior and extension of the exterior por- 

 tions of the whole thickness of the gun : — 



^09. 1 and 2 aro shell-guna. 



76. Even were we to adopt Sir H. Douglas's coefficient of expansion for the 

 24-pounder, and apply it to the 32-pounder, the gun having the smallest wind- 

 age of any in the Table, the shot would still have 0'0348 of windage left; and, 

 as the values of a in the empirical formula frequently used for obtaining the 

 velocity of shot — 



F=1600 



lac 

 4w' 



