and the Double Refraction of Insulatina Fluids. 7 
In sulphide of carbon the electric double refraction remained 
the same when the temperature varied 10°. 
When insulating fluids are examined between two concen- 
tric cylinders with a Babinet compensator, so that the dark 
streak in the compensator appears parallel to the lines of elec- 
tric force, on the electrification of the fluid the dark streak is 
the more displaced the nearer it lies to the inner cylinder. It 
frequently at the same time forms a curve with a turning- 
point, running to different sides according to whether the fluid 
possesses positive or negative double refraction. I have some- 
times observed this turning-point even with strong electric 
forces between plane electrodes. 
The difference of rate of light polarized parallel and that 
polarized perpendicular to the lines of electric force, at the 
surface of two cylinders with internal radius B^ and external 
radius E 2 , and length I, is given approximately by the equa- 
tions 
,7-B l P 1 
(r x log nat. ^) 
B^ 
(6) 
100 (R 2 lognat,5 
B x is mostly found smaller, B 2 greater, than the constant B, 
under otherwise like conditions. B x and B 2 are likewise in 
general found to be smaller the greater the length of fluid 
through which the light passes. 
For a series of fluids with cylindrical electrodes of 10-47 
centim. length and 0*3-0*5 centim. internal, 07 centim. ex- 
ternal radius, I obtained, as means of several series of experi- 
ments, the following results : — 
Electric Double Refraction for various Fluids between Cylin- 
drical Electrodes, measured with a Babinet Compensator. 
(Fraunhofer's line D.) B^'10 6 . B.,.10 6 . 
A. "X. 
Iodine and sulphide of carbon . . . 53*69 
1 part sulphur + 4 parts sulphide of") 90.55 43-05 
carbon J 
Sulphide of carbon 22*50 33*65 
Heavy benzol 4*21 6*49 
Oil of turpentine 3*15 4*55 
Petroleum 0*60 
Colza oil -2*81 -7*00 
Oil of rape-seed —2*07 
Ether 4*17 -6*82 
