206 C. Barns — Viscosity of Solids. 



Considering the permanent effects of temperature on the 

 residual magnetic induction of hard saturated steel, Dr. 

 Strouhal and I* found it necessary to discriminate between 

 two species of magnetic loss : 



(1) The direct effect due simply to thermal action on the 

 magnetic configuration ; 



(2) The indirect effect, due to the action of temperature in- 

 producing mechanical annealing. 



These two kinds of loss of residual induction often occur 

 together. Considered separately the latter, cost, par., is very 

 decidedly the greater in amount, and its character fully typified 

 by the concomitant phenomenon of mechanical annealing. 

 The former (1) is not only much smaller in relative magnitude, 

 but subsides completely within a much smaller interval of 

 time. In general, the occurrence of permanent magnetism in 

 hard steel, in its thermal relations is subject to nearly the same 

 laws of variation as those adduced in §§ 9 to 13, for ordinary 

 mechanical strains. Instability of the carbon configuration is 

 more seriously detrimental to magnetic permanence than is 

 instability of thermal configuration. 



If the unstable carburation configuration be removed by 

 thorough annealing at 100°, then the cold hard re-saturated 

 magnet must show exceptionally good magnetic stability as 

 regards the effects of mean atmospheric temperature. If the 

 saturated magnet is again thoroughly annealed at 100°, the 

 exceptionally good magnetic stability in question is even 

 further enhanced, because the magnetic configurations unstable 

 as far as 100°, have now also been removed. Experiment 

 shows the second magnetic loss to be relatively small. The 

 rods carry the maximum of permanent hardness and the maxi- 

 mum of permanent magnetization as far as 100°. This process 

 of consecutive annealing is the one we proposed when the 

 magnets made are to withstand the effects of atmospheric tem- 

 perature, of percussion, and of secular time.f 



20. In the above paragraphs I have referred to thermal, 

 carbon, and magnetic configurations, using the adjectives 

 merely to designate the chief cause of the instability under 

 special consideration, whereas the configurations themselves 

 were not necessarily different. In the same way I contrasted 

 thermal and motional instability. Thus a carbon and a thermal 

 configuration may be one and the same grouping, considered 

 from different points of view ; so may a thermal and a magne- 

 tic configuration. The latter phrase is used advisedly, and the 

 rod showing residual magnetic induction supposed to consist of 

 configurations of all degrees of magnetic stability, as well as 



* S. and B.: Wied. Ann., xx, p. 662. 1883. 



f Details in Bull. U. S. G. S., No. 14, chapter VI 



or 1. c. 



