involved in the Construction of Artillery. 291 



greater thickness to the voussoir bars, or to the single cylindric tube which 

 may constitute the interior of the chase of the gun. 



285. In guns cast or forged soHdly, of one piece, and of the usual propor- 

 tion of one caliber in thickness, 



e^D" 

 and 



D' = ?, D" 



and the areas of resistance on the length I, are as 4 : 1, which is the ratio of 

 the tendency to longitudinal rupture, to that for transverse rupture, in guns of 

 the established models. 



286. It is indispensable, that the radial joints between the voussoir bars, be 

 made originally closely fitting, and that the total extension of the external rings, 

 at the moment of maximum pressure, be not such, as shall sensibly open them, so 

 as to admit the momentary pressure of the elastic gases of the powder between; 

 if this happen, it is practically the same thing as if the caliber of the gun were, 

 for the instant, enlarged by an increase of diameter, equal to twice the thickness 

 of the longitudinal bars, and the bursting strain may be thus greatly increased, 

 in the same way, as fracture, once begun in the interior of a solid cast gun, adds 

 its own depth to the diameter of the piece, as affected by the bursting strain 

 (sects. 3 and 4, and Note X). This may be best secured by dividing the internal 

 longitudinal bars into two equal thicknesses, one within the other, breaking 

 joint longitudinally, so as to diminish the radial depth of the abutting joints of 

 the innermost bars, which alone in this case can receive any pressure from the 

 explosion. 



287. Thus arranged, and with a properly proportioned strength of gun, this 

 difficulty may be fully provided against ; for example, in a 10-inch gun, thus 

 made, assuming the mean circumference of the external shrunk-on rings to be a 

 little more than 6 feet, their total extension at the instant of its maximum (which 

 will be after that of maximum pressure) should not exceed q^Xhj of their total 

 length, = -012 of an inch ; and supposing the whole circumference divided into 

 15 equal voussoirs, or bars, the extent of opening for the instant between each 

 would be '0008 of an inch, less the lateral extension of each voussoir, produced 

 by their compression in the normal, under the force. This will probably be about 



