THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Aet. XXXIX. — Torsional Magnetostriction in Strong Trans- 

 verse Fields and Allied Phenomena / by C. Barus. 



1. In 1885 Kirchhoff* published his remarkable research on 

 the effect of stress on magnetization. This is the most com- 

 prehensive treatment which the problem has received and 

 agrees in its applications with the deductions of Lorbergf and 

 of Korteweg^: for the analogous cases of electrostriction. It is 

 well known that Maxwell's§ original stresses refer to a medium 

 without structure. A subsequent generalization of von Helrn- 

 holtz| makes the stresses in the electric or the magnetic field 

 dependent on changes of density in the medium while Kirch- 

 hoff's stresses allow for a dependence both on bulk and on 

 elongation. These stresses thus contain three constants, the 

 first of which is either the susceptibility or the permeability of 

 the medium (with the corresponding constants for dielectrics) 

 according as in the original statement the magnetization or the 

 magnetic induction is to be expressed in terms of the field. 

 His second and third constants correspond to the bulk expan- 

 sion and elongation in question. If the third constant is 

 annulled, Kirchhoff's stresses coincide with those of von Helm- 

 holtz ; if the two new constants are annulled Maxwell's stresses 

 may be reduced. Other great authors^ (J. J. Thomson, 

 Hertz) have contributed to the subject in similar ways. 



* Kirchhoff : Wied. Ann., xxiv, p. 52, 1885. 



f Lorberg: Wied. Ann., xxi, p. 300, 1884. 



\ Korteweg: Wied. Ann., ix, p. 48, 1880. 



§ Maxwell: Electricity; § 105, p. 146, vol. i; § 644, p. 255, et seq., vol. ii. 



I Helmholtz: Wied. Ann., xiii, p. 400, 1881. 



"([ The present meager account will suffice, since an excellent digest of the sub- 

 ject has been given in a paper by Nagaoka and E. Taylor Jones in Phil. Mag., (5), 

 xli, p. 454, 1896. 



Am. Jour. Sci. — Fourth Series, Vol. X, No. 60. — December, 1900. 

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