PROCEEDINGS OF THE POLYTECnNIC ASSOCIATION. 657 



block, the central fissures are usually attributed erroneously to rounding 

 the block,) to twice its length in the large pile, yet there is no fibre ; in 

 fact, tlie crystalization closely resembles the crystalization in'other masses 

 of the same material, made up in the ordinary manner by welding the 

 original blooms, from which the small bars were made and massed together. 



95. The only advantage got by this laborious process is in being assured 

 of more perfect homogeneity, there being no extensive planes of weakness. 

 I have also noticed very little difference in the transverse or longitudinal 

 tensile strength, except at the centre, subjected to the cooling strains that 

 promote fissures, which can be partiall}' avoided by extremely slow cool- 

 ing, but by leaving the whole mass porous. 



9G. Having tlius shown the fallacy of adhering to the present received 

 systems, and the difficulties attending the fabrication of large wrought- 

 iron guns, I will now show how I have endeavored, as a first effort, upon 

 an entire new system, to make a gun not liable to failure from any of the 

 foregoing causes, and will give the description a^ found in Ilolley's Work 

 on Ordnance, page 327. 



THE WIARD GUN AS DESCRIBED IN HOLLEY's WORK. 



97. Mr. Wiard's Plan. — Mr. Norman Wiai-d, whose ingenious and im- 

 portant speculations on the bursting of guns by the heat of firing have 

 been referred to in the foregoing chapter, has received a large order for 

 heavy cannon, based upon the endurance of either one of two test guns. 

 The engravings, to be found in the Transactions of the American Institute 

 for 1862, on pages 430, 431, illustrate the general features of his plan, but 

 not the exact proportions; these are the subject of extended experiments 

 and calculations not yet perfected. 



98. The gun is said to have the same diameter and length of bore as the 

 navy 15-inch gun, and about nine inches greater external diameter, and is 

 to weigh 43,000 pounds. The interior parts may be cooled uniformly by 

 water passing through the cores between the ribs, and in the bore, upon 

 Captain Rodman's plan. The exterior part or reinforce being thicker than 

 the other parts, will cool last after casting, and is by this means intended 

 to compress the barrel with such force as to bring all parts of the metal 

 into equal strain at the instant of firing, according to Professor Barlow's 

 formula. The ribs are curved in both directions, from front to rear, and 

 from the inner barrel to the outer hoop or reinforce, so that they can spring 

 enough to allow the .inner bari'el, to expand both longitudinally, and the 

 intention is, radially, by the heat of firing, without straining the struc- 

 ture. Tlie ribs also yield, during the process of casting, under unequal 

 contraction, due either to unequal cooling, or to chemical difference in the 

 metal. They are proposed to be stifi" enough to resist the pressure of 

 the powder, and sufficiently flexible to bend under the greater force of 

 expansion, a force limited only by the ultimate strength of the metal. The 

 elasticity of the whole structure would be greater than that of guns with- 

 out ribs. 



99. This gun will undoubtedly cool without serious initial rupturing 

 strains. The whole practice in founding, especially in founding car-wheels, 

 (which a cross-section of the gun resembles,) warrants this conclusion. 

 A plain disk wheel, not annealed, can only be stretched or compressed, 



