Brown — The Change in Young's Modulus of Nickel. 189 



The changes are smaller, or about 3 per cent., for the alternating fields of 

 frequencies 25 and 50 per second. 







20 4-0 60 



Magnefac Field. 



80 



Fig. 1. 



Section II. 



Transverse Magnetic Fields. 



In this part of the investigation the arrangement of the apparatus was 

 the same as in the previous part, with the exception that the solenoid was 

 replaced by a slotted iron tube. The transverse magnetic fields were pro- 

 duced in the gap of a soft iron tube by means of five insulated copper wires 

 running down inside the tube. The iron tube had a slot cut through the 

 wall along its whole length of 215 cms., the tube being 2'54 cms. external 

 diameter, 1/6 cm. internal diameter, breadth of face of slot 0'47 cm., and 

 width of slot 0'8 cm. The copper wires were well insulated from each other 

 and from the iron tube, and were placed so that four wires were grouped 



