462 On the Thermal Conductivity of Water. [Apr. 3, 



Armand de Quatrefages, Georg Hermann Quincke, Theodor Schwann, 

 and Jean Servais Stas were balloted for and elected Foreign Members 

 of the Society. 



The following Papers were read : — 



I. « On the Thermal Conductivity of Water." By J. T. Bot- 

 TOMLEY, Lecturer in Natural Philosophy and Demonstrator 

 in Experimental Physics in the University of Glasgow. 

 Communicated by Professor Sir Wttjjam Thomson, LLD., 

 F.R.S. Received March 11, 1879. 



(Abstract.) 



The experiments described in this paper were undertaken at the 

 instance of Sir William Thomson and by a method devised by him. 



The liquid whose thermal conductivity is to be determined is heated 

 from above, to avoid convection currents. Two methods of heating 

 have been used. In one, a horizontal steam chamber is applied at the 

 top of the water or other liquid ; and, steam being continuously passed 

 through the heating chamber, the surface of the liquid under experi- 

 ment is kept at a very high temperature, and heat is conducted from 

 above downwards. In the other method a large quantity of very hot 

 water is deposited on the top of a mass of cold water, mixing being 

 prevented by a simple contrivance ; and the heat of this super- 

 incumbent layer is conducted downwards through the colder water 

 below. 



The experiments have been carried on in very large vessels, or 

 tanks, in order to avoid disturbance by means of loss of heat at the 

 sides. It is intended, at the suggestion of Professor Clerk Maxwell, 

 to observe the loss of heat by the sides under given circumstances, 

 and to estimate, from results of such experiments, the probable error 

 due to this loss. 



In the experiments three principal thermometers are employed; 

 together with a fourth, whose object is merely to show when heat 

 begins to be lost at the bottom of the layer of fluid experimented on. 

 When this loss commences the experiment is at an end. The other 

 three thermometers are used thus : — First there is a thermometer 

 with a bulb 30 centims. long. It is placed vertically ; and its object 

 is to show the average temperature from top to bottom of the layer of 

 fluid bounded by horizontal planes passing through the top and 

 bottom of its bulb. The rise of this thermometer in any time shows 

 the quantity of heat that has passed into the stratum occupied by it 

 in that time. The other two thermometers are placed with their 

 bulbs horizontal, and one at a known distance vertically above the 



