I 



" On Galvano-Hysteresis. (Preliminary Notice.)" By 

 SILVANUS P. THOMPSON, D.Sc., B.A., Professor of Physics 

 in the City and Guilds Technical College, Finsbury. 

 Communicated by Professor G. CAREY FOSTER, B.A., B.Sc., 

 F.R.S. Received March 16, 1891. 



91.] Prof. S. P. Thompson. On Galvano- Hysteresis. 439 



results than can be often obtained by assuming that a so-called non- 

 inductive circuit is really non-inductive, and, therefore, that the 

 apparent power is the true power. 



[. If a sufficiently strong electric current is passed through a coil 

 insulated soft iron wire for a short time, and the wire then discon- 

 nected, and if, after the lapse of any length of time, the wire is placed 

 in the circuit of a galvanometer, and is then subjected to longitudinal 

 magnetisation or to a succession of alternately directed longitudinal 

 magnetisations, it is found to discharge an electric current through 



I the galvanometer. 

 2. The direction of the current discharged from the iron wire is 

 found to be the same as that of the current which was originally 

 ised through it. 



The direction of the discharge current is opposite to that in 

 ich the discharge current would flow if the wire acted as a 

 condenser. 



4. A wire which has once produced such a discharge current will 

 not produce a second unless again traversed by a charging current. 



5. A wire which has not been subjected to any, preliminary process 

 of charging, that is to say, one which since being annealed has not 

 been traversed by an electric current, does not sensibly show any such 

 phenomena, either when subjected to longitudinal magnetisation or 

 to a succession of alternate magnetisations. 



6. The sense of the discharge current is quite independent of the 

 direction of the longitudinal .magnetisation used in producing the 



isturbance which effects the discharge. 



7. The time-integral of the discharge current is independent of the 

 ration of the charging current, provided this is not too suddenly 



turned off. It increases with the strength of the charging current 

 up to a certain limit, being proportional to it through a certain range 

 of values, but is not proportional to it for currents below or above 

 certain limits of strength. These limits vary with the gauge of the 

 wire, but are independent of its length. For a charging current of 

 jriven strength the discharge current from a given wire is greatest 



I if the charging current is gradually reduced to zero and not abruptly 

 broken by a spark. 

 8. The time-integral of the discharge current is practically inde- 

 2 G 2 



