92 Profs. J. A. Fleming and J. Uewar. On the 



at low temperatures. The soft annealed iron if cooled slowly to 

 185 C. recovers its original permeability when heated up again to 

 ordinary temperatures. The unannealed iron, however, after cooling 

 to the same low temperature, retains some of its increased perme- 

 ability when heated up again to 15 C. The unannealed iron cannot 

 be taken over the temperature range again and again with the same 

 definite permeability values at each recurrent temperature, as in the 

 case of the soft annealed iron. The unannealed iron is more or less 

 permanently changed in magnetic character every time it is heated 

 or cooled. 



With this transformer, a long series of observations were taken to 

 determine the hysteresis loss corresponding to different inductions 

 when taken at the ordinary temperatures, and the temperature of 

 liquid air. The hysteresis cycles were taken with the ballistic 

 galvanometer over wide ranges of maximum induction, the trans- 

 former being alternately at the ordinary temperature and in liquid 

 air, but no constant magnetic condition could be obtained. In one 

 set of observations, at a given maximum induction the hysteresis loss 

 was increased when the transformer was raised in temperature, and 

 for another series of observations at the same induction it was 

 diminished. It is therefore impossible to make any definite state- 

 ment with regard to the magnetic hysteresis loss in this unannealed 

 iron ring coil at the two temperatures. The mere fact of immersing 

 the unannealed iron in the liquid air changes its magnetic qualities 

 to such a degree that it is no longer the same material, magnetically 

 considered, after, as before its immersion. One curious fact, however, 

 was noticed very soon with regard to unannealed iron, and that is, 

 that if the unannealed iron ring coil has a small magnetising current 

 passed through its primary coil, the secondary coil being connected 

 to the galvanometer, the sudden immersion of this ring coil into 

 liquid air invariably causes a deflection of the ballistic galvanometer, 

 even when the primary magnetising current remains perfectly con- 

 stant in value, thus showing a sudden and very large increase in the 

 permeability of the unanneaied iron. Whilst the iron is in the 

 liquid air it retains this increased permeability. If brought suddenly 

 out its permeability again diminishes, but not with equal rapidity. 

 This is partly accounted for by the fact that the iron is cooled with 

 immense rapidity when it goes into the liquid air, but it heats up 

 again much more slowly when it is brought out. The definite fact, 

 however, remains, which has been repeatedly observed, that the 

 cooling of this unannealed iron to a low temperature always increases 

 its permeability, as far as we know, no matter whatever may be the 

 magnetising force employed. One difficulty experienced in dealing 

 with unannealed iron is the fact that in taking it up to the high 

 magnetising forces, and by the process required to remove residual 



