76 Magnetic Qualities of Iron. [June 15, 



being in the form of rings. The iron examined was, for the most 

 part, thin sheet metal or wire such as is used in the construction of 

 transformer cores. The experiments show that there are marked 

 differences in the values of jHcZI in different specimens, some nomin- 

 ally soft iron requiring two and even three times as much work to be- 

 spent in reversing its magnetism as is required in the best iron. 

 They show, further, that great permeability does not necessarily 

 imply small hysteresis losses. The order of merit in a group of 

 samples is not the same when permeability is made the criterion of 

 magnetic softness as' it is when the smallness of JHdl is made the cri- 

 terion. 



In connexion with these results a formula proposed by Mr. C. P. 

 Steinmetz (JEM = cB 1 ' 6 )* to express the relation of the hysteresis 

 losses to B is discussed, and it is shown that although such a formula 

 may serve fairly well as an approximate statement of the relation 

 within those limits of B which are important in practice, it fails when 

 applied to the more extreme portions of the curve. 



The authors go on to describe a second group of experiments, in 

 which direct measurements were made of the heat developed in mag- 

 netic reversals. The method consisted in using two rings, alike in 

 all respects, with divided magnetising coils. One ring had its coils 

 coupled so that the two parts opposed each other, and the core was 

 consequently not magnetised when a current passed. The other ring 

 was active, and its coils (coupled inductively) were connected in 

 series with the non-inductive coils of the inactive ring. Alternating 

 currents were passed through both, and the active ring became heated 

 by the effects of hysteresis and Foucault currents. To balance this a 

 steady current was caused to flow in the core of the inactive ring, and 

 the energy expended in the magnetic reversals of the active ring was 

 found by measuring, the energy which had to be expended in this cur- 

 rent in order that the temperature of the two rings might continue 

 equal. In some cases the rings used were miniature transformers, 

 and the test was applied to see whether the energy expended in mag- 

 netic reversals remained the same when the secondary of the trans- 

 former was closed as when it was open. This question had been 

 raised by more than one experimentalist in relation to tests of the 

 efficiency of transformers. The authors could not detect any difference 

 in the amount of energy consumed in the core when the " load " was 

 taken off or put on the secondary. 



In a third group of experiments the magnetic curve tracer was used 

 to examine certain features of the curves of magnetisation. This in- 

 strument, invented by one of the authors, draws curves which exhibit 

 the relation of the magnetisation of given samples of iron or steel to 

 * ' Trans. American Inst. of Electrical Engineers,' yol. 9, Ko. 1. 



