. Currents in Wires subjected to Mechanical Strain. 343 



It will be observed that the direction of the current changes 

 just before the wire breaks. 



Some steel wire was now taken ; and as it was found almost 

 impossible by the most careful annealing to get a piece of wire 

 arranged in the apparatus which should give no deflection 

 before the application of the weight, the initial deflection was 

 noted in each case. 



Experiment 3. — A steel wire *81 millim. diameter. © = 16°. 

 Initial deflection = 20 S.U. W = 31'5. After the application 

 of the weight the deflection reversed its direction to U.S. The 

 result is given in the following Table. 



Time D 

 (minutes). 



2 10 



3 12 



4 13 



5 15 



6 18 



24 .... . 10 



25 9 



50 9 



90 5 



130 3 



The apparatus was then left for about 90 hours with the 

 weight attached ; © being still 16°, there was now a deflection 

 of 15 S.U. The weight was then removed, and the deflection 

 fell rapidly and changed to U.S. The subsequent deflections 

 were as follows: — 



Time from removal D. 



of strain (minutes). U.S. 



1 2 



2 3 



3 4 



4 6 



5 7 



6 8 



14 8 



20 10 



25 7 



30 3 



In both cases we observe that the current gradually rises to 

 a maximum and then falls. 



Experiment 4. — A steel wire *98 millim. diameter. © = 15°. 

 Initial deflection = 10 S.U. On the addition of a weight of 



