Longitudinal Stress on the Magnetization of Nickel. 119 



It consisted of two hollow cylinders of 2"5 centim. radius. 

 The lower cylinder was fixed to a tripod stand, while the 

 upper one fitted into it, and was movable. The latter was 

 graduated on its external cylindrical surface at intervals of 

 20°, and by means of a pomter which was cut on the corre- 

 sponding surface of the fixed cylinder the amount of twist was 



easily read ofi". The screw, S, attached to the lower cylinder 

 serves to fix the upper one at any desired angle of twist. On 

 the inner surface of the movable cylinder two vertical V- 

 grooves were cut opposite each other. On these the two ends 

 of the thick brass diametral rod were made to slide. This 

 rod had a small hole at its centre which was just large enough 

 to allow the passage of the brass wire attached to the lower 

 end of the nickel wire. In order to secure the axial position 

 of this hole with reference to the twisting-cylinder, the rod 

 was fixed between the V's and bored on a lathe by turning it 

 together with the cylinder. A small clamping-screw served 

 to pin the wire fast against the side of the rod, so that the 

 wire and cylinder rotated together. 



