Interactions of Circular and Longitudinal Magnetizations, 245 



in circuit with the solenoid and set close to the magnetometer. 

 The wire was then inserted, and subjected to cyclic variations 

 of magnetic force. The magnetizing current was changed 

 continuously from a given positive value to an equal negative 

 value, and back again to the original positive value. The 

 variation was effected in a gradual manner by means of a 

 liquid rheostat, consisting of a column of dilute sulphate of 

 zinc with zinc electrodes, through which a steady current 

 from a battery of Daniell cells was constantly flowing. By 

 means of a sliding zinc electrode, the necessary current was 

 shunted through the solenoid circuit. The tangent-galvano- 

 meter included in this circuit was of course far removed from 

 the solenoid, and was so placed that the operator, in adjusting 

 the rheostat, could easily read the galvanometer-deflexion. 



In the earlier experiments careful attention was paid to the 

 first effects, as well as to the permanent cyclic condition which 

 soon becomes established after a few cyclic changes of the 

 magnetizing current have been gone through. At suitable 

 stages in the variation of the current, the current was kept 

 steady until the corresponding deflexion of the magnetometer- 

 needle was observed and noted. These remarks will suffice at 

 present to indicate the general method adopted in studying 

 the cyclic changes, which have been so fully investigated by 

 Warburg and Ewing. 



One of my objects was to study the modification produced 

 on this cycle and on whatever else may be associated with it, 

 when a current is passed along the magnetized wire. This 

 linear current (as we shall call it) was derived from one or 

 more Bunsen cells. It entered the iron wire at the end 

 furthest removed from the magnetometer and returned along 

 two copper wires stretched parallel to the iron wire and very 

 close to it. 



A complete set of experiments consisted in : — 



(1) Taking a permanent magnetic cycle when no linear 

 current was flowing along the wire. 



(2) Observing the initial effect when the linear current was 

 made to flow in one direction along the wire, and taking 

 the permanent magnetic cycle with this current kept 

 steady. 



(3) Observing the initial effect when the linear current was 

 broken, and taking again the permanent magnetic cycle 

 as in (1). 



(4) Observing the initial effect of the linear current put on 

 in the other direction, and taking the permanent mag- 

 netic cycle with this current steady. 



(5) Operating as in (3). 



