708 Prof. L. T. More on the Fatigue of 



capacity being thereby introduced. It appears, in fact, that 

 for assemblages of electrons to be able to give rise to a 

 dielectric capacity different from that of free sether, the con- 

 stitution of the electron must be assumed to involve electric 

 displacement so great that electric displacement and electric 

 force are no longer linearly related. It is not to be supposed 

 that this would involve (for example) non-linearity of the 

 equations of optics : in radiation traversing free sether, as 

 already explained, we are dealing with values of electric 

 displacement which could still be well within the limits of 

 sensibly linear relation; while the optical phenomena exhi- 

 bited by (say) ordinary transparent media would fall within 

 the category of small oscillations about a configuration of 

 equilibrium, or about a state of quasi-steady motion, and 

 would accordingly be deducible from linear equations. In 

 this connexion it is not even necessary to take account of the 

 circumstance that each individual electron, notwithstanding 

 the non-linear strain- relations involved in its constitution, 

 would obey (for moderate velocities) very simple laws of 

 motion. As a rough general analogy it may be helpful to 

 consider a thin spring laterally loaded to such an extent that 

 the relation between the load and the resulting deformation 

 is not even approximately linear. None the less the small 

 oscillations of such a system about a position of equilibrium 

 will be isochronous, and deducible from a system of linear 

 equations. 



22. Some progress has recently been made towards a static 

 conception of atomic structure, and in relation to such theories 

 especial significance attaches to questions regarding the 

 possible non-linearity of electro-magnetic relations, with cor- 

 responding modification of the law of force between electrons 

 placed in close proximity to one another. 



LXIL The Fatigue of Metals subjected to Rdntgen Radiation. 

 By Louis T. More, Ph.D., Professor of Physics in the 

 University of Cincinnati *. 



SINCE the discovery of Hallwachs that metals grow less 

 sensitive to ultra-violet light after long exposure to the 

 rays, many attempts have been made to determine the cause 

 and laws of this "photo-electric fatigue." Some discrep- 

 ancies in the results still exist, but there is general agree- 

 ment that it varies with the kind of metal used, the state of 

 the surface, the gas in which the metal is placed, and the 

 character of the rays. We know so little about the nature 



* Communicated by the Author. 



