the Investigation of Young's Modulus for Wires. 555 



In fig. 15 the two types of field-elongation curve are given 

 for a cycle through the range of field used in the above 

 experiments, viz., from + 47 to — 47 o. G. s. units. The 

 ordinates are elongations of the wire expressed in half wave- 

 lengths of sodium light, the abscissas give the current in the 

 solenoids in amperes, and are therefore proportional to the 

 field. The continuous line is the curve for a specimen of 

 soft iron with a load of 3000 grms. on the three No. 22 b.w.g. 

 wires; the dotted line is the curve for hard pianoforte-steel 

 with a load of 20,000 grms. In each case the left half of 

 the curve is higher than the right, which may possibly be 

 due to a rise of temperature during the experiment, perhaps 

 due to hysteresis. jVv 15. 



T 



2 AMP 



-4 



The second cycle in Table B is interesting ; it shows 

 that for that load the wire is in a transition state, and for the 

 lighter loads the state of affairs is similar to that indicated in 

 the upper half of the cycle, while for heavier loads the type 

 of curve is that given by the lower half. 



It will be noticed that in the above examples the elongation 

 is considerably greater than the contraction, so that the net 

 result of a cycle is an elongation. This might be due to a 

 gradual rise in the temperature, owing to the heating of the 

 solenoids, or it might mean that the fact of reversing the 



