458 



Prof. Quincke. 



[Dec. 16, 



I am not aware that residual charge has been observed in any liquid 

 dielectric. 



The results obtained by Professor Quincke are not easy to recon- 

 cile. For that reason it is the more desirable that their full signifi- 

 cance should be ascertained. Full information is given of all the 

 details of his experiments except on one point. It is not stated 

 whether, in the experiments for determining K by direct discharge of 

 the condenser, the capacity of the connexion and key was ascertained. 

 It would in most ordinary arrangements of key be very appreciable 

 in comparison with the capacity of the condenser itself. If neglected 

 the effect would be to a certain extent to give too low a value of K, 

 the effect being most marked when K is large. 



I have made a few preliminary experiments to determine K for 

 colza oil with several different samples, and both with continuous 

 charges and intermittent charges from an induction coil. The values 

 of K range from 2'95 to 311. Professor Quincke's results in his 

 first paper are K=2'443, K^=2-385, K,=3-296. 



The property of double refraction in liquids caused by electrifica- 

 tion is sometimes cited as showing that electrification is not propor- 

 tional to electromotive force. The fact that the double refraction in 

 a liquid under powerful electromotive forces is very small would 

 further show that there is a close approximation to proportionality, 

 and that the deviation from proportionality would be insensible to any 

 electrostatic test. Such conclusions, however, cannot be safely drawn 

 in the case of bodies such as castor-oil, in which Kd=/t 2 . In such 

 bodies, assuming the electromagnetic theory of light, the yielding to 

 electromotive force is much greater if the force be applied for such 

 time as 10 -4 second than when applied for 10~" u second, and it is 

 quite possible that the law of proportionality might be untrue in the 

 former case, but very nearly or quite true in the latter. 



" Addendum to Dr. Hopkinson's 4 Note on Specific Inductive 

 Capacity.'" By Professor Quincke, For. Mem. R.S. 

 Received December 5, 1886. 



Notiz uber die Dielectricitatsconstante von Flussigheiten, 

 von G. Quincke. 



Bei Gelegenheit einer Untersuchung der Eigenschaf ten dielectrischer 

 Fliissigkeiten (' Wiedemann, Annalen,' vol. 19, 1883, p. 707 ; vol. 28 

 L886, p. 529) hatte ich die Dielectricitatsconstante mit der electrischen 

 Wage oder dem hydrostatisch gemessenen Druck einer Luftblase 

 grosser gefunden, als mit der Capacitat eines Condensators, der von 

 Luft oder isolirender Fliissigkeit umgeben ist, und beim Umlegen 

 eines Schlussels durch einen Multiplicator entladen wird. 



