550 Intelligence and Miscellaneous Articles. 



in this subject actually tried, and its result is as negative as all the 

 optical ones have been. I am not prepared to admit that there 

 ought to be a first- order effect ; but anyhow the experiment is an 

 interesting modification of the thermopile experiment suggested in 

 1833 by Fizeau, which so far as I know has not yet in that form 

 been attempted. 



It happens that Herr des Coudres in the same communication 

 suggests the possible aberration of a mountain-top as seen from a 

 valley, referred to in a footnote to § 32 of my paper. 



I would also take this opportunity of mentioning a mathema- 

 tical memoir by Professor H. A. Loren^, " La Theorie Electro- 

 magnetique de Maxwell, et son application aux corps mouvants," 

 which appeared in the Archives JS T eerJandaises, vol. xxv, in 1892. 

 There are also various short communications by Mr. Heaviside 

 on the same subject in his collected papers. 



Yours faithfully, 



October 28th, 1893, O ,iyer J. Lodge. 



ON A SIMPLE METHOD OF INVESTIGATING THE CONDLCTING 

 POWER OF DIELECTRIC LIQUIOS. BY K. R. KOCH. 



In recent times many investigations have been made as to the 

 coexistence of dielectric power and electrical conductivity. Engaged 

 myself on an investigation in which I desired to ascertain quali- 

 tatively the power of insulation, I have found the following method 

 very useful and rapid in its execution. 



If it be assumed that electrical conductivity in dielectric liquids 

 is of the nature of electrolysis, we must look tor galvanic polari- 

 zation in two electrodes inserted in it and connected with a 

 galvanic battery. In ordinary circumstances this could not of 

 course be galvanometrically or electrometrically measured. Yet 

 a capillary electrometer, in which the electrolyte is the liquid 

 itself to be investigated, may in a suitable manner be made so 

 sensitive that the existence of a polarization, and therewith of 

 electrolytic conductivity, may be demonstrated. An ordinary 

 Lippmann's capillary electrometer could not be used for this 

 purpose ; Dewar's * form is much more sensitive. This consists 

 of a horizontal tube about 1 mm. in the clear, winch on each side 

 is connected with mercury cups ; the mass of mercury in the tube 

 is separated by a drop of dilute sulphuric acid, if the instru- 

 ment is to be used in the ordinary way for measuring electrolytic 

 forces ; in the present case the dilute acid was replaced by a drop 

 of the substance to be investigated. If, now, the two mercury cups 

 are connected with the poles of a battery the drops move in one 

 way or the other, according to the direction of the current, if the 

 liquid conducts electrolytically, and thus when polarization takes 

 place at the opposite surfaces of the mercury. 



* < Nature/ vol. xv. p. 210 (1877). 



