Sir W. Thomson on Mr. Varley's Reciprocal Electrophorus. 287 



it is obvious that many other data must be taken into account. 

 These are notably the thickness of the layer of liquid at W, the 

 capacity for heat of the various liquids, the relative volumes of 

 the vessel B and its tube, &c. 



Arranged in the order of quantity of heat conducted, it ap- 

 pears from these experiments that the following bodies are in 

 the following order : — 



Mercury 333 



Water 270 



Oil of turpentine .... 230 



Glycerine 216 



Iodide of amyl .... 200 



Nitrobenzol 1701 



Aniline 170 J 



On obtaining these well-marked differences, innumerable sug- 

 gestions at once offered themselves — such as the employment of 

 a thermoelectric pile in place of the air-thermometer. And 

 some of the results gathered from this prolific field I propose to 

 communicate subsequently. 



London Institution, 

 March 16, 1868. 



XXXIII. On Mr. C. F. Varley's Reciprocal Electrophorus . 

 By Sir William Thomson, LL.D., F.R.S* 



HAVING been informed by Mr. Fleeming Jenkin that he 

 had heard from Mr. Clerk Maxwell that the instrument 

 which I described under the name " Replenisher," in the Philo- 

 sophical Magazine for January 1868, was founded on precisely 

 the same principle as an instrument "for generating electri- 

 city " which had been patented some years ago by Mr. C. F. 

 Varley, I was surprised ; for I remembered his inductive machine 

 which had been so much admired at the Exhibition of 1862, and 

 which certainly did not contain the peculiar principle of the 

 "Replenisher." But I took the earliest opportunity of looking into 

 Mr. Varley's patent (1860), and found, as was to be expected, that 

 Mr. Maxwell was perfectly right. In that patent Mr. Varley de- 

 scribes an instrument agreeing in almost every detail with the 

 general description of the " Beplenisher " which I gave in the 

 article of the Philosophical Magazine already referred to. The 

 only essential difference is that no contacts are made in Mr. 

 Varley's instrument, but, instead, the carriers pass, each at four 

 points of its circular path, within such short distances of four 



* Communicated bv the Author. 



