142 Mr. Mallet on the Physical Conditions 



beginning of last century the caliber of cannon for both land and sea service 

 was reduced, perhaps, much below the middle point of prudence. 



The paper of Mr. Kobins, published in 1746, entitled "A Proposal for new 

 Arming the British Navy, by boring out all the eighteen pounders to guns of 

 larger caUber," was perhaps the iirst step towards that return to artillery of the 

 largest caliber, which characterizes our own day. The progress of these views, 

 the constant consolidation in construction of fortified places, and improvements 

 in the strength of ships of war, have all tended to increase the size of modern 

 artillery, resulting, amongst other improvements, in the Paixhan and Lancaster 

 guns, the use of hollow shot, &c. (Note B.) 



2. During the ages occupied by these mutations, gunpowder itself has — 

 through the greater purity of its constituents, greater skill in proportioning and 

 combining them, and improved methods of preserving and of firing— been greatly 

 increased in power ; and hence our modern artillery of enlarged caliber is fre- 

 quently subjected to a strain in service greatly exceeding anything to which 

 the ancient enormous cannon were exposed, throwing stone shot of light spe- 

 cific gravity compared with iron balls : and which the confessedly great im- 

 provements in the manipulation of metals in recent times have as yet scarcely 

 been able fully to cope with. (Note C.) 



3. In considering the strains to which a gvm is exposed when discharged, and 

 limiting our views to the mere pressure upon its interior, produced by the elastic 

 gases of the inflamed powder, it is obvious from consideration of the formula 

 giving the relation between this pressure and the resistance of the cylinder of 

 the gun, 



p.D"^R{D'-D") = 2Be. ■ (1) 



In which, 



p = the pressure per square inch on the interior of the cylinder ; 

 D' and D" — the external and internal diameters respectively ; 

 i2 = the coeiBcient of cohesion of the substance of the gun ; 

 and e — the thickness of the gun. 



That the value of ^, the pressure per square inch, at its maximum point 

 (wherever that may be, between the first instant of ignition, and the balls leav- 



