480 MEMOIR OF DANIEL TREADWELL. 



layers of particles in the walls -vvhicli were supposed to constitute in very large 

 cannon natural hoops at different distances from the bore, may render very thick 

 walls a cause of weakness instead of strength* Mr. Treadwell's conclusions were 

 subsequently fully sustained in practice. 



Mr. Treadwell also pointed out a fallacy in Captain Rodman's estimate of the 

 pressure on the walls of his gun by the fluid produced by fired gunpowder, as 

 measured with an instrument of his invention. The instrument consists of a small, 

 but strong iron frame, having a .shank or plug forged upon one of its sides. This 

 plug is one and a half inches in diameter, and one and a half inches long, and 

 is formed into a screw, the thread of which corresponds with a similar screw- 

 thread cut into the outer portion of each of several holes fourteen inches apart, 

 extending from near the breech towards the muzzle. A small hole is bored 

 through the axis of this plug, making a free passage to the calibre of the gun. 

 A piston is nicely fitted to this hole in the plug, and thus the end of the piston, 

 receiving the whole of the force of the fired gunpowder, will be driven outwards 

 at each discharge. A large steel head or block is fitted upon the outer end of 

 the piston, and from this head rises a lozenge-shaped point. Against this point, 

 and firmly fixed in the frame, is a piece of thick copper, in which an indentation 

 is made by the point at each discharge. The depth of this indentation is then 

 compared with that made by a known pressure of weights made upon a similar 

 tool, and from this comparison Captain Rodman infers the amount of the fluid pres- 

 sure of the fired gunpowder on the walls of the cannon. Mr. Treadwell showed 

 that the movable mass of matter composing the instrument was fired against or 

 into the copper, as much as the ball is fired out of the muzzle of the gun. The 

 pressure to which the instrument is subjected changes its inertia into living force, 

 and causes it to display and register double the force which is applied to it. 



" Captain Rodman seems, indeed," says Mr. Treadwell, " to have had no suspicion of 

 any error when his instrument gave indications of a force wholly incompatible with the 



* " On the Practicability of constructing Cannon of Great, Calibre, capable of enduring long continued Use 

 under full Charges," Memoirs of the American Academy, 185(5. 



"A careful examination by Russian engineers of cross sections of the Rodman gun shows that it frequently 

 happened that the least contracted layer was very near the walls of the bore ; sometimes, indeed, the latter are 

 not only not contracted, but are actually under a slight strain of extension. M. P. Holostov abandoned the natural 

 hooping of cannon extolled by Rodniau, and recommended hoops of steel for all snch cannon manufactured at Penn, 

 or at the Oboukhnff works." Notes on the Construction of Ordnance, No. 21, Washington, May 14, 1683, p. 8. 



According to the Report to the United States Senate by the Joint Committee of February 1.5, 1800, it 

 appears that 23 of Rodman's cast-iron rifles bur'Jst in service; 10 burst spont.aneonsly ; 5 of them burst in the 

 lathe, one with the report of a six-pounder; two burst while standing in the pit at the foundry. Of 43 Rod- 

 man 15-inch guns cast for the Navy, which was the greatest number in service at any one time, 17 have 

 burst or been disabled. 



