52 ON THE CONSTRUCTION OF HOOPED CANNON. 



original length on being released from the strain. On carrying the strain, how- 



ever, to 280 pounds, the wire became permanently elongated, as was shown, on 

 its release from the strain, by the small quantity denoted by the distance from the 

 zero line of the short line immediately under it; while the permanent elasticity 

 was shown by the distance of the two short lines from each other (as seen over 

 the number 280). The operation was then continued by successively giving to 

 the wire, and again removing from it, the loads of 320, 360, 400, and 440 pounds; 

 and the effects are graphically shown in the figure by the distances between 

 the zero line and the nearest short lines, which distances represent the perma- 

 nent elongations, while the distances between the short lines themselves repre- 

 sent the permanent elasticity, after the strain of each load. 



The register-plate was then moved upwards a little upon the rod, and a 

 new zero line, B, (Figure 2) was marked upon it. With this I began as 

 before, by placing npon it a strain of 40 pounds, and then, in succession, 80, 

 120, 1G0, 200, 240, 280, 320, 360, 400, and 440 pounds; removing each in like 

 accession, to see if any permanent elongation would be produced by this repe- 

 tition of the strain. As might have been expected, none whatever was pro- 

 duced, but the ruler returned in each case to the zero line, as shown in the 



figure. But, on increasing the strain to 480 pounds, the elongation shown at c 

 "was produced. 



Knowing that the strain had reached nearly the limit of the strength of the 



matenal, I then subjected the wire to the heat of two largo pieces of iron, 



heated to a gWg red, and passed, one above and one below, in contact with 



h, ,nre. By this means the wire was heated to sneh a degree that oil burned 



iv, ly, on being dropped upon it, through its whole length. The wire was 



kept connected, m -its place, with the apparatus during this heating operation, and 



.I W " 1,kCW1Se k *P* strai S ht V a tension of 40 pounds from the steelyard. 

 The temperature to which it was raised could not have been less than 850. 



i ! 1Z 7 ' resister -P ,ate and *e ruler, which had been removed, 



T \ ?". * ^ a MW »» line > C ' ™ -rked. (Sec Figure 3.) 



": zs^zs^sti T rem ;r ftom the ^ - h ^ -* 



resneciv, L*_ 1"!™*" Mrked ' as sh °™ « the figure, above the 



! pective numbers. N 



480 pounds, the ,a,ne re ul t 1 7 w" ™ V ™ *» * ^ "* ° f 



■ • nni,W 7 , , WM before reached - Th e elasticity, therefore, 



nmmpau-ed by the heating. But. Ok tod ~* «, , .,- L.-„.. ™« 



renui 



near the teusile strength of Z ' *** ° f 48 ° P ° Unds beiDS ^ 



™gw ot the wlre , on mcreasi it tQ 520 , stretch 



g li iv o^u me g 



shown 



