454 H. Nagaoka and E. T. Jones on the Effects 



Lord Salisbury, in his address before the British Association 

 at Oxford, 1894, remarks : — " Oxygen constitutes the largest 

 portion of the solid and liquid substance of our planet, so far 

 as we know it ; and nitrogen is very far the predominant 

 constituent of our atmosphere. If the earth is a detached bit 

 whirled off the mass of the sun, as cosmogonists love to tell 

 us, how comes it that in leaving the sun we cleaned him out 

 so completely of his nitrogen and oxygen that not a trace of 

 these gases remains behind to be discovered even by the 

 sensitive vision of the spectroscope?" 



Although we have not succeeded in detecting oxygen in 

 the sun, it seems to me that the character of its light, the 

 fact of the combustion of carbon in its mass, the conditions 

 for the incandescence of the oxides of the rare earths which 

 exist, would prevent the detection of oxygen in its uncombined 

 state. Notwithstanding the negative evidence which I have 

 brought forward, I cannot help feeling strongly that oxygen 

 is present in the sun and that the sun's light is due to carbon 

 vapour in an atmosphere of oxygen. 

 Jefferson Physical Laboratory, 



Harvard University, Cambridge, Mass., U.S. 



XLIX. On the Effects of Magnetic Stress in Magnetostriction, 

 By H. Nagaoka and E. Taylok Jones*. 



MATHEMATICAL expressions for electric and magnetic 

 stresses were given first by Maxwell in his ' Electricity 

 and Magnetism.' In Art. 105 of this treatise the values are 

 found of stresses in a dielectric medium, which may be re- 

 garded as producing the observed electric action between two 

 systems ; in Art. 644 corresponding expressions are found 

 for a magnetic medium. The expressions in the two cases 

 are, however, not similar ; i. e. the electric stress in a dielectric 

 cannot be deduced from the magnetic stress in a magnetic 

 substance simply by substituting specific inductive capacity 

 for magnetic permeability. It does not seem quite clear 

 whether Maxwell intended his expressions to apply to the case 

 of induced as well as rigid magnetization. 



In 1881, v. Helmholtz f published expressions for the stresses 

 which are more general than those of Maxwell, since they 

 contain terms depending on possible changes of density in 

 the medium. These expressions were assumed to have the 

 same form for a dielectric as for a temporarily magnetized 

 substance, but not necessarily for a permanent magnet ; and if 



* Communicated by the Authors. 



t Wied. Ann. xiii. p. 400 (1881) ; or Abh. i. p. 798. 



