286 



Messrs. C. G. Lamb and W. G. Wilson. 



ri 



for this quantity, where ? x and / 2 are the lengths, ri and r 2 the radii of 

 the pots. This gives for A the value 1560 when the lengths are 

 measured centimetres. If W denote the rate of supply of energy in 

 watts, the rate of transference of heat in gram-C "-units when the 

 steady state is attained will be H = 0239 W. Hence, if c is the 

 specific conductivity, and 6 the temperature gradient, 



H = 1560 c$; 



therefore c = 0-000153 — . 



6 



Two points had to be settled before the determination could be 

 evaluated : — (1) Whether the temperature was uniform over both 

 copper pots ; (2) whether any part of the temperature gradient was 

 due to a sudden drop at the surface of separation. As regards the 

 outer pot, since it is wholly surrounded by water, its temperature* 

 must be uniform, and the inside and outside can only differ by the 

 drop through the copper, which is eliminated by putting the junction 

 inside that pot: to test the question as regards the inner pot (and 

 partly as regards the outer one) junctions were placed at various 

 points on the surfaces, as well as at certain other points, as shown in 

 Fig. 2. The result of this experiment is given below. 



Junction. 



1 



2 



3 



4 



5 



6 



7 



8 



9 



Temperature 

 relative to S 



25 -6 



25-6 



25 4 



25 2 



13 -8 



0-6 



0-6 



o 



28-1 



It will be seen that the temperature over the surfaces of the pots 

 was practically imiforni, and hence the determination of the gradient 

 could be satisfactorily determined from readings taken with one junction 

 on each pot, as at first described. 



The second point was tested as follows : — A third pot was provided, 

 having a clearance of 1 inch with regard to the former larger pot ; 

 under similar conditions as to character of insulator and power sup- 

 plied the temperature gradients in the case of the two combinations of 

 small and medium, and small and large, pots were measured ; the ratio 

 was found to be - 5-±. The value of A for the new arrangement of 

 small and large pots was calculated, and found to be S±0 in centimetre 

 measure, being thus 0*538 of the standard combination. The close 



