AND LIQUIDS AND THEIR VARIATION WITH TEMPERATURE. 405 



The heat conducted away by the wire per second 



= qk -, for x = 0, 



= \/qk . ph . VQ. 



For the copper wire used (No. 28), p = '15, allowing for silk covering ; h = "0003, 

 q -0011, and k = I'D, therefore 



Vqk.ph = 2'2 X 10~ 4 . 



For the platinoid wire, which had the same diameter, we have k = 'OS, and 



\/qk.ph = '6 X 1CT 4 , 



therefore total loss of heat along thermo-wires from one disc per second 



= 2-8 X 10~*. v . 



If w is the thickness of a disc which would lose the same amount of heat from its 

 edges, we have, since the loss of heat from such a disc = 2-irrwhv Q , 



2-8 x 10-* 2-8 x 10-' 



W = ^T = 12-6 x 3 x 10- = >075 C6ntimS ' 



and the loss along the thermo-wires may be taken into account in the theory of flow 

 of heat in the discs, by taking as the thickness in the formula, p. 403, the measured 

 thickness of the disc plus this quantity. 



Constants of the Discs. 



r = 2 centims., therefore irr 3 = 12'5 sq. centims. 

 10 = '075 centims. 



Z M = '32 + -075 = '395 centims., therefore 1 + < M + *?- = 1-395 + -T. 



r 4 4 



t c = -103 + '075 + '055* = -233 centims., therefore 1 + t c = 1-233. 



r 



t v = -312 + -075 + -055* = -442 centims., therefore n + 4r = '442 + %-. 



T & i 



* Half tbe thickness of the heating coil and mica insulation is added to the upper disc and half to 

 the cover. 



