ON THE CONSTRUCTION OF HOOPED CANNON. 53 



shown in the figure, above this number and immediately below the zero line, wa>« 

 produced. Still, on taking off the load, the wire exhibited its old elasticity, and 

 this even a little increased. This load, replaced and continued for six hours, carried 

 the elongation much further, as shown in the figure ; and so nearly Mas the 

 breaking-point reached, that the elongation continued even after the load was 

 reduced to 500 pounds, and the wire finally broke after it had been elongated 

 the ^st part of its length under a strain of 510 pounds, thus showing a tensile 

 strength of 75,120 pounds to the square-inch area* The permanent elasticity 

 had reached, just before the fracture, or when the load was 480 pounds (equal 

 to 70,700 pounds per inch area), j\ of an inch, or the ^Igth (.00214) part of 

 the length of the wire- Other experiments were made by exposing the wire, 

 which was the subject of them, to the heat of melted lead. Here, in two 

 cases, the wire was passed slowly under the surface of lead which was kept 

 very much above its melting temperature. These wires, when tried afterwards 

 in the testing machine, showed their previous elasticity unimpaired. 



The fourth experiment that I shall relate, was made upon a piece of wire 

 from the same hank with that before used, after it had been annealed to a 



■ 



full red heat. This, after having been straightened, was placed upon the testing 

 machine, and subjected to a succession of strains, commencing at 40 pounds, and in- 

 creasing by steps of 20 pounds each (instead of the 40 pounds before used) up to 

 320 pounds, under which strain the wire broke ; thus showing an ultimate tenacity 



of 47,128 pounds per square inch, or, allowing for the diminution of the area 

 of the wire by the elongation previous to breaking, about 51,000 pounds, instead 

 of 75,120 pounds, as given in the former case. The permanent elasticity had 

 reached, just before the fracture, or when the load was 300 pounds upon the wire 



(or 44,186 pounds per square inch), T W of an inch > or the Vis tn P art of the 

 original length of the wire. The effects of the various increasing strains are 

 fully exhibited in Figure 4 (next page), which (as is also true of the preceding 



figures) 



The following numbers represent the weight upon the wire when reduced, or computed, for a square 

 bar of one-inch section: 



40= 5,891 200 = 29,458 360 = 53,025 520 = 76,592 



80 = 11,783 240 = 35,350 400 = 58,917 560 = 82,433 



1 20 = 1 7,675 280 = 41 ,2 41 440 = 64,808 



160 = 23,596 320 = 47,128 480 = 70,700 



VOL. IX. NEW SERIES. - 8 



