232 Dr. D. K. Morris on the Magnetic Properties 



he made on a sample of transformer plate of similar thickness 

 and obtained from the same firm as the author's were. The 

 maximum permeability was about 4500, while the hysteresis 

 varied from 740 down to 580 ergs for B=+4000; and 

 attention is drawn to these values as representing the best 

 iron both as regards high permeability and low hysteresis 

 which he had tested. It is therefore of interest to note that 

 specimen B had after annealing at 1150° a maximum per- 

 meability of over 4600 at ordinary temperatures, and a hys- 

 teresis as calculated for B= +4000 of just under 500 ergs, 

 corresponding to a hysteresis loss of but -295 watts per lb. at 

 a frequency of 100^. The following values are taken from 

 the magnetization curve at 24° C. : — 



B. 



H. 



fi. 



2000 



•74 



2700 



4000 



1-01 



3960 



6000 



1-33 



4520 



8000 



1-82 



4400 



10000 



2-84 



3520 



12000 



5-63 



2130 



Between 0° and 200° the diminution of hysteresis with rise 

 of temperature is *08 per cent, per degree, when the limits of 

 induction are kept constant. 



W. Kunz * concludes from his experiments that for soft 

 iron the hysteresis is expressible as a linear function of the 

 temperature. This is not in accordance with the author's 

 results. The curves expressing this relation (Nos. 16) for 

 specimen B are far from straight, and show a decided dip at 

 about 500° corresponding to the minima which occur near 

 that temperature on the permeability-curves. 



III. Resistance-Temperature Curves. — The variations of 

 specific resistance with temperature are shown graphically on 

 curves 17 and 18. 



By taking a sufficient number of observations (see Tables 

 XI. and XII.) the author has been able to show that the 

 resistance-temperature curve undergoes no abrupt change of 

 direction at or near the critical temperature. (Previous ob- 

 servers have given curves all of which were broken at this 

 temperature ; an examination of the figures given by Hop- 



* W. Kunz, ' Elektrotechnische Zettschrift,' 1894, p. 196. 



