THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. YII. — Apparent Hysteresis in Torsional Magnetostric- 

 tion, and its relation to Viscosity ; by C. Barus. 



1. In the present paper I shall describe a series of phe- 

 nomena bearing on the permanence of torsional magnetostriction 

 in iron and nickel magnetized by circular and by longitudinal 

 fields, which have been encountered in different ways by 

 others, but which appear here not only with greater clearness 

 and in a more elementary form, but in a manner indicating a 

 certain uniformity in the behavior of all metals. The phe- 

 nomena are evoked by purely magnetic action. They are 

 obtained by twisting the wire alternately back and forth over 

 a definite angle within the elastic limits and examining the 

 change of rigidity produced by circular or by longitudinal 

 magnetization immediately after each new twist and after 

 several repetitions of the magnetizations. The first magneti- 

 zation succeeding any twist operates on the magnetic configu- 

 rations surviving from the preceding twist and magnetizations ; 

 the remaining magnetizations (current alternately made and 

 broken) for the same twist operate on the new configurations 

 produced by the twist in question and the first magnetization 

 applied to it. The results are very different as the following 

 observations show. The former are viscous (temporary), the 

 latter elastic (permanent) in character. 



To explain the phenomena I shall make use of Maxwell's 

 theory of viscosity in which (as I have ventured to interpret 

 it) any deformation due to molecular instability is a viscous 

 deformation. !Now when the breakdown is gradual in char- 

 acter, which it must be if dependent on temporary local inten- 

 sities in the distribution of heat motion, the deformation will 

 be gradual as actually observed in ordinary viscous phenomena. 



Am. Jour. Sci.— Fourth Series, Vol. XI, No. 62.— Febeuary, 1901. 



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