[ 31.3 ] 



XLIII. Intelligence and Miscellaneous Articles. 



ON LIGHT-ABSORPTION ACCORDINCt TO MAXWELL's THEORY. 

 BY C. H. C. GRINWIS*. 

 '^PHE author, in continuation of Maxwell's few remarks on tbe 

 -■- connexion between the strong absorption of light in metals and 

 their high conductivity for electricity, has further pursued them 

 theoretically : — 



Let a plane electrical wave in a body move in the direction of the 

 a'-axis \A-ith a velocity Y and amplitude A. Then let the resulting 

 vibrations take place parallel to the ^/--plane and be parallel to the 

 s-axis ; let K and /u be the specific induction-capacity of the body 

 for electricity and magnetism, its conductivity C, X the wave- 

 length ; further, for brevity, let h be = ^, and H the magnetic 



moment along the z-axis. If lu denotes the current-intensity, then, 

 according to Maxwell (Treatise on Electricity and Magnetism, vol.ii. 

 p. 394), putting ;iK = rt^ 27r/iC = 6^ 



dx dt^ dt 



If this equation satisfies a periodic function of the time, 

 H=Ae-/'* cos Tc {x—^t), 

 it thence follows that 



so that 



H = Ac-2.rMCV.- cos h{x-Yt). 



If we now calculate from Maxwell's general formulae (1. c. art. 

 638) the energy contained by the unit of volume of our body in con- 

 sequence of the above vibrations, we get (since the quantities P, Q, 

 E, and Gr there occurring are =0 when the vibrations are parallel 

 to the z-n.xis, while H is only a function of cc, u, t) 



rt = a=c=7=0, 

 dx ' 



Q__ld^ 



fj. dx ' 



and the electrostatic potential energy E and the electromagnetic 

 actual energy T become : — 



^^S-X-dTJ' 



S7rfx\dxJ' 



* Verslagen en Mededeclingen d. Kong. Ak, van Wetenschappen te Am- 

 sterdam, Natunoiss Ahth. (2) x. pp. 371-383. 



