Effects of Mechanical Stress on Electrical Resistance. 287 



56 Ibs. attached to the other end. While this weight was on, 300 

 complete turns were made in the wire, the density being measured 

 after 200 turns, and again after 300 turns. It was found that the 

 wire had stretched by about 23 per cent, after being thus treated. 

 -The density, as will be seen, increased very slightly about J per 

 cent. 



Density before twisting = 8'850 



after 200 turns = 8'887 



300 =8-896 



A twist of 300 turns in a length of 130 cm. represents 2'3 turns 

 per centimetre. 



This wire was also tested for alteration of torsional rigidity and 

 Young's modulus by Mr. J. E. Monroe, with the following results : 



Length of wire = 425 cm. 



Heating. 



A preliminary trial was made on the effect of heating. The wire 

 which had been used in the experiments just described was raised to 

 a white heat by an electric current, to find out if by this means the 

 density could be brought back to its original value which it had 

 before being twisted. The heating, however, did not seem to alter 

 the density appreciably, the difference not being more than ^ or 

 iV P er cent. 



Effect of Hammering. 



A piece of copper wire was flattened by heavy blows with a hammer, 

 and the density measured. The hammering was then continued, and 

 the density again measured. 



Density of original wire = 8'866 



after first hammering = 8 '868 

 second hammering = 8'875 



