782 



SCIENCE. 



[N. S. Vol. IV. No. 100. 



the material accummulated, having value to 

 the expert engineer and corroboratory of 

 those conclusions. In the opinion of the 

 writer, the latter may be accepted as thor- 

 oughly well-established. 



E. H. THUKSTOisr. 



COENELIi UNIVEESITY. 



ON CERTAIN PHYSICAL DIFFICULTIES IN 

 THE CONSTRUCTION OF LARGE GUNS. 



The substitution of forged steel for cast 

 iron in gun construction has resulted in the 

 universal adoption of the built-up gun. 

 About the year 1855 the Englishman, 

 Blakely, and the American, Tread well, in- 

 dependently discovered and demonstrated 

 the value of the principle of initial tension 

 as a means of increasing the strength and 

 economizing the material of a gun. What 

 this means can be briefly shown. 



Assume a tube of perfectly annealed 

 metal with given tenacity and elasticity. 

 If a powerful stress be applied, there is no 

 reason why one part should be more capa- 

 ble of resisting it than another. Let the 

 tube be closed at one end, and let the stress 

 originate from within near this end, as in 

 the explosion of a charge of gunpowder. 

 Under this condition it was shown by 

 Treadwell that if we assume the tube to 

 be made up of a large number of uniform, 

 cylindrical, concentric layers of metal, then 

 the resistance of each layer to the explo- 

 ding force will vary inversely as the square 

 of the diameter. The stress in its effect 

 upon the metal decreases at a rate quite 

 similar to that of the radiation of heat or 

 light. If the wall of the tube be under no 

 initial stress its inner surface may be 

 stretched even to its elastic limit, while the 

 stretching of the outer surface is compara- 

 tively slight. The metal's property of elas- 

 tic resistance is hence not utilized to the 

 best advantage in the outer layer, while 

 in the inner layer it may be utilized to an 

 extent inconsistent with safety. 



Treadwell therefore proposed a plan of 

 gun construction which has since been, uni- 

 versally adopted. The modern gun con- 

 sists of a steel tube which is reenforced by 

 one or more concentric hoops or tubes, the 

 number and position of these being adjusted 

 to the variation of pressure from within as 

 the hot exploding gas finds vent at the 

 muzzle. The ordinates of the pressure curve 

 are greatest at the origin, this being taken 

 as the middle of the seat of the powder 

 charge in the chamber. They decrease 

 rapidly with approach to the muzzle. The 

 reenforcement of the tube should therefore 

 be greatest around the breech. A tubular 

 jacket is shrunk on around the main tube, 

 covering the breech and often as much as 

 two-thirds of the entire length. Around 

 the jacket is a series of compressing hoops, 

 and around this there may be a second or 

 outer series of supplementary hoops. Origi- 

 nally the interior diameter of the jacket is 

 a little less than the exterior diameter of 

 the tube. By heating the jacket sufficiently 

 it is made to expand until large enough to 

 be slipped into place over the cold tube. 

 This becomes enormously compressed by 

 the subsequent cooling of the jacket. In 

 like manner the first hoop is too small to 

 be slipped over the cold jacket until suffi- 

 ciently heated for this purpose. The same 

 remark applies to the relation between the 

 second and first hoops. The final result is 

 that the diameters of the tube, both ex- 

 ternal and internal, are permanently de- 

 creased by the compression of the jacket, 

 while those of the hoops are permanently 

 increased. Their contractile force is not 

 enough to compress the jacket into smaller 

 space, for this itself is pushed outward by 

 the powerful reacting force of the com- 

 pressed tube within. The hoops, therefore, 

 serve to reenforce the jacket by their own 

 tendency to contract. Having been put on 

 in an expanded condition and prevented 

 from recovering their normal dimensions, 



