230 Mr. W. M. Mordey. On Sloiv Changes [Jan. 17, 



increase in the power-factor indicates a possible (but improbable) 

 increase in the eddies, such as would be accounted for by a decrease 

 of the specific resistance of the iron. The author is proceeding to 

 investigate this matter by continuously heating a ring formed by 

 winding a volute of iron ribbon or wire, overwound with a testing 

 coil of copper wire. The ends of the iron being brought out enable 

 measurements of the resistance to be taken, the magnetising losses 

 being measured as in the other samples.* 



Magnetisation not necessary to Production of the Effect. Having 

 ascertained that neither magnetic nor electric action was necessary to 

 the production of this effect, the author has endeavoured to find 

 whether alternate- current magnetisation of iron can be carried on 

 -continuously, or for considerable periods, without producing any 

 noticeable change, and, although the evidence is not sufficient to 

 justify a positive statement, he finds that so long as the iron is kept 

 cool it suffers no reduction of permeability. For example, a trans- 

 former in regular use for certain testing purposes, and used several 

 hours daily during the last fifteen months, has kept its permeability 

 unaltered. It is magnetised at various densities up to about 2700 B. 

 It is a specially designed apparatus, of large size for the work it has 

 to do (and therefore inefficient and costly), and the temperature of its 

 iron probably never rises more than about 6 to 8 C. above the room 

 in which it is placed. It may be that its daily periods of rest account 

 for the absence of change. This supposition is, however, not sup- 

 ported by other cases where iron which has been in regular use, but 

 with daily periods of rest, has shown the increase of hysteresis very 

 clearly. 



Condition not Changed by Repose. Further, the iron of some trans- 

 formers which showed this increase, but which for several months 

 have not been used, shows no return to the original condition. The 

 author is therefore inclined to believe that if periods of repose in 

 some cases prevent the rise, it is because the time of use is not long 

 enough to allow of much increase of temperature. 



This part of the subject is being pursued, but for the present the 

 author will only say that, so long as iron is only slightly warmed 

 (even when that warmth is caused by alternate-current magnetisa- 

 tion) its permeability remains unaffected. 



It may be that repose at a temperature near or below zero, Centi- 

 grade, or at a still lower temperature, would have some effect. It 

 appears possible, since continued expansion due to moderate heat can 

 bring about this permanent increase of hysteresis, that continued 

 contraction by moderate cold may bring the iron back to its original 

 condition, or even permanently increase its permeability. The author 

 Intends to investigate this point. 



* See Appendix II, p. 241. 



