368 Prof. J. Larmor on the Influence of 



independent of the Earth's motion, if the form of the consti- 

 tutive relation which connects electric polarization with electric 

 force, for the material medium, is not altered by its convection; 

 but. not reflecting that reversal of the direction of light in a 

 moving medium alters its wave-length, a hasty inference was 

 made that this negative deduction represented the negative 

 experimental result long ago announced as probable by 

 M. Mascart. 



I understand that Prof. Lorentz assents to, or at any rate 

 admits as probable, the application of the principle (which 

 rests indeed on a development in the molecular direction of 

 his own previous analysis), that uniform convection does not 

 affect the constitution of a permanent material system formed 

 of groups of electrons or material ions that interact by electro- 

 dynamic agency alone; except in so far that, instead of the 

 ordinary time, we must refer the convected system to a new 

 time-variable, the u local time " of Prof. Lorentz. The con- 

 stitutive relations of a rotational medium, as well as all 

 properties depending on extinction of light, form a case in 

 point. Considering radiation propagated in the direction of 

 the axis of the rotational quality of the medium, say the 

 direction of x, the relation between the material polarization 

 (0, g', //) and the electric force (0, Q, R) in its undulations 

 is expressed ('iEther and Matter/ p. 211) in the form 

 , K-l^ 1 / 8 d 



9 = 



1/6 d\ Ti 



47TC 2 



7/ K-l^ 1 / h d\ r 



47rc- 47rc 2 \ l dt ax) 



in which the coefficient e 2 represents the structural and e 1 the 

 magnetic type of rotation. When the material medium, 

 instead of being at rest, is being convected in the direction of 

 cc with velocity v, this structural relation should thus remain 

 true when for t is substituted the local time t' (Joe. cit. p. 168) 



equal to t— —x, so that every function </>(#, t) becomes 



<f>(x,t 2^)' * ms k ee P s ~J7 unaltered, but changes — 



into l^r — -o 77 ) 6. Thus the effect of the convection will 

 \dx c 2 dt) r g 



be to maintain the coefficient of magnetic rotation e 1 -r- 



d l 

 unaltered, but to change the structural coefficient e v *-j- into 

 i j dot 



the mixed type c 2 -j e 2 -^ ji ; and the equation of electric 



constitution of the medium being thus modified, the rotation 

 produced by it remains unaltered by convection. This is, in 



