422 DR. C. H. LEES ON THE THERMAL CONDUCTIVITIES OP SOLIDS 



t m = thickness of copper disc below glass, plus correction for thermo-wires, 



T L = radius of disc of liquid, 



t, = thickness of disc of liquid, 



v v = excess of temperature of upper disc over that of the air in the enclosure. 



V M = excess of temperature of middle disc ,, 



Vj, = excess of temperature of lower disc ., ,, 



then the heat flowing through the glass disc per second 



= TTT~KQ - , 

 the heat entering the middle disc 



and the heat leaving the middle disc by its under surface 



t G 4 



The amount passing through the disc of liquid 



the amount entering the ebonite ring surrounding the liquid may be put * 



where A is an unknown constant depending on the breadth of the ring under the 

 middle copper disc, and on the distribution of the lines of flow in it. Between these 

 quantities we have the relation t 



from which we can determine k t if A, k Q and h are known, by observations of v v , V K , 

 and V L . 



* Strictly, a term Bv L ought to be introduced here, since some of the lines of flow from the middle 

 disc may pass through the ebonite to its upper surface. On account of the smallness of B, this 

 term has been neglected. 



t See note, p. (403). 



