C. Barus — Inversion in the Wave Mechanism, etc. 343 



Akt. XLIII. — A Curious Inversion in the Wave Mechanism 

 of the Electromagnetic Theory of light / by C. Barus. 



1. The account given by the equations of the electromag- 

 netic theory of light as to the motion, is without ambiguity; 

 but when one endeavors to reconstruct such a wave graphically 

 one is apt to fall into a trap such as will make the wave run 

 backwards. To briefly summarize the formulae relevant to the 

 present paper, I will refer to the mode of derivation in which 

 the conception of a displacement current conditioned by the 

 time variation of electric force is first clearly put. Then the 

 fundamental equation for electric flux in the direction of an 

 axis (Y) in terms of the line integral of magnetic force (a, 7) 

 around that axis is in the usual notation 



K_ bY__ 6a _ by 



~V ~bt~bz bx ' ' 



provided the Hertzian device of measuring electric quantities 

 electrostatically and magnetic quantities eleetromagnetically is 

 introduced for symmetry. Here V is the normal velocity of 

 light, K the specific inductive capacity of the medium. A 

 clockwise curl of magnetic force around the electric axis is 

 therefore in question. 



On the other hand, the fundamental surface integral of mag- 

 netic flux in the direction of an axis (2), is expressed in terms 

 of the line integral of electric forces around that axis by 



V bt ~ bX by K } 



where Hertz's method has again been used and where /* is the 

 magnetic permeability of the medium. The curl of electric 

 force around the magnetic axis is here counter-clockwise. 

 Further equations need not be adduced since the electric 

 forces X and Y in directions x and y and magnetic forces <z, 7 

 in directions x and z at the point x, y, z and at the time t, suf- 

 fice for the present purposes. 



From these equations to the differential equations of wave 

 motion, known in form and treated with success even in 

 D'Alembert's time, is not an arduous span. Making it one 

 obtains in the usual way 



bf~fJLK V ' 



and 



b? ~ /x/iT V 7 ' 



