'358 Dr. J. R. Ashworth on the Anhysteretie 



substance, thus setting up alternating circular fields in the 

 metal, except in one group of experiments in which it was 

 led into the surrounding solenoid, the alternating field thus 

 acting to and fro in the direction of the magnetizing field. 



(3) All the experiments have been carried out by the 

 magnetometric method. It has the advantage over the 

 ballistic method that it allows the observer to watch any 

 change of magnetization continuously instead of inter- 

 mittently. The magnetometer was an astatic one with a 

 pair of vertical needles 0*7 centimetre apart and 13 centi- 

 metres in length suspended by a long silk fibre within a 

 stout copper tube. The deflexions of the astatic pair were 

 read by the usual arrangement of a reflected beam of light, 

 the scale being about 1*7 metres from the mirror. 



In the experiments on iron the solenoid was placed 

 horizontally east and west and in such a position that its 

 axis was on a level with the upper pair of poles of the 

 needles, but in the experiments on nickel the vertical position 

 was chosen in order to obtain a suitably large deflexion, and 

 to minimise disturbances in the compensation due to certain 

 thermal effects. In this position the vertical component of 

 the Earth's force had to be balanced or allowed for. The 

 solenoid itself was about 30 centimetres long, wound with a 

 single layer of stout copper wire covered with asbestos, and 

 was enclosed in a tubular sheath of copper, the whole being- 

 supported on two brass uprights. 



When the apparatus had to be heated a row of broad flat 

 Bunsen flames was applied underneath, the iron or nickel wire 

 being suitably supported in the solenoid ; on the other hand, 

 when the wire had to be kept cold during the passage of a 

 strong alternating current it was placed in the solenoid inside a 

 glass tube through which a stream of cold water was allowed 

 to flow. Each wire was 20 centimetres in length and was 

 attached at one end to a stout piece of brass wire insulated 

 with an asbestos sleeve ; this brass wire served the double 

 purpose of supporting the iron or nickel wire and of affording 

 a return path for the alternating current. The iron wire 

 was 0*057 centimetre in diameter and the nickel wire 0*050 

 centimetre, so that the dimension ratio was not less than 

 350. 



When everything was in adjustment a continuous current 

 was supplied to the solenoid the strength of which could be 

 varied by means of a potentiometer, and the alternating 

 current employed to annul hysteresis was derived from a 

 generator having a frequency of 33 alternations per second. 



