Electro- optic Observations on various Liquids. 229 



of the metals, for which (with few exceptions) a. lies between 

 0*0036 and 0*0038. In the supposition that a part of this dif- 

 ference is to be accounted for by the strong magnetism of iron 

 we shall be confirmed when we consider that (with the excep- 

 tion of platinum) the lowest value of a belongs to bismuth, the 

 most strongly diamagnetic metal — namely, 



a =0*0035. 



1 have here selected only a few points, which show a rela- 

 tion to the question in hand in the most direct and striking 

 manner. The reader who is intimate with the theories con- 

 cerning it will find in other departments also, e. g. in the 

 beautiful investigations of Gr. Wiedemann on the connexion 

 between galvanic currents, torsion, and magnetism, multifa- 

 rious points in which a connexion with the foregoing analyses 

 is recognizable. 



The carrying-out of my experiments in the laboratory of this 

 University has been much furthered by the willing assistance 

 of Professor Meyer, for which I here express my gratitude. 



Breslau, 2oth June, 1878. 



XXVI. Electro-optic Observations on various Liquids. By John 

 Kerr, LL.D., Free Church Training College, Glasgow. 



[Continued from p. 102.] 



31. \ITE come now to the fixed oils. Two of these (olive and 

 ▼ » castor) had been already examined carefully in the 

 old cell — the former with good effect, the latter not. The fixed 

 compensator is now withdrawn; but all the other arrangements 

 are as formerly for CS 2 (6, 7). The principal difficulty of 

 electro-optic experiments on liquids (the obtaining of a suffi- 

 ciently clean charge) is now much aggravated. Sometimes 

 the method of working already described (2) is not perfectly 

 adequate, except at the expense of much time. Even when 

 every known precaution has been taken, and charge after 

 charge of the same oil passed through the cell, there are often 

 a few visible specks left in the liquid, either solid particles or 

 small bubbles, which interfere materially with the observations. 

 But even in such cases, I generally get a pure and regular 

 effect by taking a line of sight a little above or below the axal 

 part of the field. And when the specks are very few, and the 

 electro-optic action of the liquid not extremely feeble, the 

 regular effect is often obtained at the centre of the field clearly 

 enough, though it is always marred more or less by the pre- 

 sence of the solid particles or bubbles. 



32. Olive-oil, the purest obtainable from the apothecaries — 

 Phil. Mag. S. 5. Vol. 8. No. 48. Sept. 1879. R 



