50 ON THE CONSTRUCTION OF HOOPED CANNON. 



might take place in the frame, in the bolts, in the steelyard, or in the wire itself 

 outside of the 140 inches comprised between the points at which the rod of the 

 register-plate and the straight-edge were respectively cramped, could not affect the 

 accuracy of the measure of any change in the wire between those points, and 

 that the straight-edge could not change its place upon the register-plate in the 

 direction of the length of the wire, unless the length of the wire itself was changed 

 in an equal degree. 



The following four experiments, made on wire of ordinary quality, from the 



same hank, will j^ive sufficient warranty to the conclusions afterwards drawn 



from them. The results here given are, as I have before remarked, altogether 



in accordance with other results obtained by the same mode of operating upon 

 other wires. 



The wire used in the experiments now given was j\°j% of an inch in diameter, 

 and, consequently, the area of its cross-section contained .006789 of a square inch. 

 Having taken a piece of this wire about sixteen feet long, hard as it came from 

 the draw-plate, I straightened it and fixed it upon the testing apparatus in the 



•plate and the 



manner before described; and, after cramping to it the register 



ruler, I commenced the operation upon it by letting the steelyard draw upon 



it with a weight of 10 pounds, for the purpose of taking out the sag, and to 



bring all the bearings into place. I then drew a line, directed by the straight- 

 edge, as before described, upon the register-plate. This line is shown in Figure 1, 

 marked Zero A. I then placed the poise of the steelyard so as to give to the 

 wire a tension of 40 pounds. This weight elongated the 140 inches of wire, 

 carrying the ruler over the register-plate the distance shown by the interval be- 

 tween the short line and the zero line at the left-hand end of the latter and 

 immediately under it; and this short line (seen above the number 40) was then 

 made by the needle-point, guided by the ruler. The poise was then removed from 

 the steelyard, when the wire returned to its original length, as was shown by 



he ruler again coinciding with the zero line. The poise of the steelyard was 

 hen placed so as to strain the wire with 80 pounds, and the distance of the short 



hue (seen above the number 80) from the zero line, shows the lengthening of 



the wtre under this strain. On removing this weh 



to 



& uuo ncijiht, the wire again returned 



ginal length ; and, on repeating the operation so as to give the wire the 



of 120, 1C0, 200, and 240 pounds, the several elongations, shown 



figure by the distances of the short 



,. , tue M10rt lmes ( se en over these numbers) from the zero 

 hue, were produced; but from each of these « Ion M ^ *. _J ™~i to 



O 



the wire recovered 



on 



ifirinal 



