408 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



moved to conform to the direction of the shot; and many have noticed, 

 when firing guns on ship-carriages, at high elevation, that the breech of 

 the gun was raised, and came down again with a considerable blow on the 

 quoin, or elevating screw. If the chase of the gun is light, the muzzle will 



•sometimes be broken off, 

 instead of overcoming the 



''\ ^^^'^^^^^^^'-^'^^^^'''''^ inertia of the gun, or lift- 



^'"■"^ ■ -" '' iiig the breech suddenly, 



C 



(■';:'.'; w-J)- V 



^ — I I against the resistance of 



the preponderance. This 

 example is inserted as one 



of the peculiarities of living force, as exhibited in gunnery, viz: resistance 

 to changes of direction by bodies in motion, and to account for the failure 

 of many of the Dahlgren and Parrott guns, from the breaking off of their 

 muzzles, as has frequently happened to the Parrott rifle guns, and to the 

 Dahlgren guns since the war began. 



From the fact that solid cast guns, of the largest size now in service, 

 have a certain strain upon them within themselves when cast, from 

 the heat leaving the inner metal last, which is relieved by the expansion 

 of the inner metal by the first few discharges, I hold that solid-cast Dahl- 

 gren guns, or any columbiads of large sizes, cast solid, may pass the 

 inspection of ten service charges, and be stronger at the tenth discharge 

 than they were at the first — that number of rounds, perhaps, being neces- 

 sary to relieve them of the beforeraentioned strain, by communicating 

 the proper proportion of heat to place them in the same state in which we 

 find the hollow cast gun at the first round. 



The guns in our service having great thickness of metal about the bore, 

 should not be relied upon in rapid firing, even when exposed to the hottest 

 rays* of the sun on their very large exterior surface — the most favorable 

 circumstances under which a gun can be fired — and should never be fired 

 at all, if a hollow cast gun with uniform density throughout the mass, in 

 rain or in cold weather. It may sometimes happen that a hollow cast gun, 

 after the Rodman plan, would exhibit greater endurance than a solid cast 

 gun, made from the same metal and at the same time. At the time of the 

 bursting of two steel 50-pounder navy guns of my fabrication, each at the 

 ninth round, at Staten Island, I suggested to the inspector either that the 

 guns should be fired at longer intervals between the discharges, or that I 

 should be permitted to give elasticity by drilling a series of small holes 

 about the bore, having a certain position relative to each other, and a 



Tia 19 



B 



proper direction to permit the expansion of the inner metal without any 

 undue strain upon the re-enforce. Captain Rodman's book, page 297, 

 exhibits the impossibility of casting a solid projectile, cavities being 

 formed in the center of the mass, due to the shrinkage of the inner metal 



