AND LIQUIDS AND THEIR VARIATION WITH TEMPERATURE. 409 



= qk-22( lOOe- 36 + 57'8e + ' 35 ) 



= '00016 X '22 ( 100 X '705 + 57'8 X 1'42) 



= -000035 (- 70-5 + 82-1) 



= '0004 gram degrees.* 



Hence, '0008 gram degrees of heat flow per second along the two wires to the 

 discs. 



Of the '21 gram degrees of heat imparted in the coil '21 X '027 = "0057 is 

 expended outside the discs, and of this '0008 is conveyed to the discs by conduction, 

 leaving '0049, or about 2'4 per cent., which does not reach the discs. The wattmeter 

 readings must therefore be diminished by this amount to give the power actually 

 imparted to the discs. 



Combining this result with the one previously found, we have for the heat, H, 



imparted to the discs, 



H = -000953 d, 



when d is the deflection on the wattmeter. 



The Thermo-electric Measurements. 



The principle adopted in measuring the electromotive forces in the various 

 thermo-electric circuits, was that of balancing them against the fall of potential 

 down a high resistance in series with a cell of known electromotive force. 



The arrangements of the circuits will be understood from the accompanying 



diagram. 



Fig. 9. 



RI, R 2 , and R z are resistances in series with the Leclanche cell, L. R 2 and R 3 are 

 resistance boxes of platinoid, of 30,000 ohms and 10,000 ohms respectively. R 3 is 

 adjustable, and it was varied until the fall of potential down the 30,000 ohms was 

 equal to that of a Clark cell, C. This adjustment was not absolutely necessary, but 

 was carried out for convenience by the arrangement shown in the figure. The thermo- 

 couple, T, is balanced against the fall of potential down a part of R lt which represents 

 three dial resistances of copper wire, only one of which is shown in the figure. The 

 movable arms of the dials consisted of short thick copper wires dipping into mercury 

 cups. The dials read respectively, ohms, '1 ohms, and '01 ohms. They were made 



* More generally the heat conducted along one wire to the discs = '0077H -000071t>, where H is 

 the heat generated in the coil, and v the temperature excess of the discs. 

 VOL. CXCI. A. 3 G 



