618 Prof. Richardson and Mr. Lownds on the Magnetic 



part of their length. The authors have been led to the con- 

 clusion thai the heating- and cooling-curves for this alloy are 

 coincident only when the highest temperature reached in the 

 experiments is considerably less than the temperature of 

 minimum permeability. When the temperature approaches 

 this value the magnetic properties of the specimen change, 

 and a new curve connecting the induction and temperature 

 is obtained. 



Table of Values of H and B at Atmospheric Temperatures. 



, 





11. 



From Observations in 1897. 



From Observations in 

 March 1900. 



H. 



E. 



H. 1 



B. 

 93 



094 



21(5 



0-6 



1-55 



469 



104 



208 



2-20 



675 



1-73 



375 



3-45 



1674 



2-88 



853 



4*40 



2200 



403 



1435 



5-39 



2614 



5-76 



2187 



6-59 



2990 



6-91 



2540 



7-82 



3294 



8-63 



2980 



8-99 



3540 



11-50 



3480 



940 



3630 



12-65 



3620 



11-19 



3906 



14-38 



3835 



13-19 



4180 



1727 



4125 



1487 



4394 



2093 



4415 



18-36 



4720 



23-85 



4620 



27-20 



5310 



26-72 



4785 



32-70 



5680 



29-60 



4975 



3300 



5670 



32-47 



5145 



In the accompanying table is given a series of values of the 

 induction and field strength at ordinary temperatures, ob- 

 tained (i.) in the summer of 1897, and (ii.) in March 1900. 



The two curves connecting them are shown as I and II on 

 fig. 4. It will be seen from these curves that the effect of 

 repeated heating and cooling is to diminish the permeability 

 of the specimen. 



Let us seek for an explanation of this unexpected result. 



It is known that impure specimens of iron containing large 

 amounts of aluminium disintegrate in course of time. It is 

 hence not unlikely that the same process is at work in spe- 

 cimens containing less aluminium, though in a less marked 

 degree. 



The microscopic examination of the specimens shows the 

 presence of crystals. 



