508 Intelligence and Miscellaneous Articles. 



ON A FUNDAMENTAL QUESTION IN ELECTRO-OPTICS. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, 



In the April number of the Philosophical Magazine Dr. Kerr 

 has published a paper, " Experiments on a Fundamental Question 

 in Electro-Optics." Dr. Kerr finds the velocity of light chauged 

 by electric stress in electrostatically strained liquids only for light 

 polarized perpendicular to the lines of force. 



My paper on the same subject is not mentioned in which, eleven 

 years ago, I treated this question with the identical methods 

 employed by Dr. Kerr. (Of. G. Quincke, " Electrische Unter- 

 suchungen, IX. Ueber die Aenderung der Brechungsexponenten 

 von Fliissigkeiten durch electrische Krafte," Wiedemann's Annalen, 

 xix. pp. 773-782, 1883.) A proof of this paper I sent immediately 

 after its publication to Dr. Kerr, who first observed the double 

 refraction of light by electric stress. 



But the results of my experiments were different from those of 

 Dr. Kerr. I observed sometimes an increase, sometimes a dimi- 

 nution, of the velocity of light whose plane of polarization is 

 parallel to the lines of force. I supposed that the reason of this 

 ambiguous change were two forces of opposite character, i. e. the 

 heating of the liquid by vortex motion and the electric pressure, 

 both excited at the same time by the electric forces. 



Heidelberg, Physical Laboratory of the G. Quincke. 



University, April 21, 1894. 



MOLECULAR ENERGY OF GASES. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, 

 With reference to the remarks made by Professor Lodge in the 

 Philosophical Magazine for April, page 419, I only need to notice 

 the chief point and to say : — It appears to me that the proposition 

 that the amounts of mechanical energy of the molecules of different 

 gases are equal, is of so fundamental a character that it ought, for 

 the advancement of science, not to be limited to algebraic expres- 

 sions readable only by mathematicians, but it should, in addition, 

 be explicitly expressed in simple words (as Avogadro's law usually 

 is) in every text-book of physics and monograph on gases, for the 

 benefit of all persons. 



I beg to remain, Gentlemen, 



Tours truly, 

 Birmingham, April 6, 1894. George Gore. 



P.S. Had the "statement" I asked for in my previous letter 

 (not an algebraic expression) existed in any of the text-books of 

 science I should almost certainly have seen it, and that letter 

 would not have been necessary. 



