CAPACITY FOK HEAT OF MKT.M.S AT DIFFERENT TEMPERATURES. 



I '_'! 



It may here be stated that the results deduced from experiments performed with 

 different pairs of thermometers were in excellent agreement, and afforded strong 

 evidence of the accuracy of the temperature measurements. 



The twin thermometers were connected in the usual manner, i.e., the coil of the 

 first in series with the compensator of the second on one side of the bridge, the 

 compensator of the first and the coil of the second being placed on the opposite side. 



For the remaining sides of the bridge, several forms of approximately equal arms 

 were used. All our later experiments were performed with two Pt-Ag coils, wound 

 together on a mica rack and placed in a brass tube containing oil, the tube itself being . 

 immersed in a constant temperature tank. Their resistances at C. were 



S, = 1533-618, S a = 1533-685. 



Their resistances could be taken separately, and were determined in ice and also 

 differentially, both at C. and at higher temperatures. Their continued equality 

 with change of temperature was remarkable. 



The galvanometer contact with the junction of S, and S a was made on a Pt-Ag wire 

 connecting their ends and situated near the bridge wire. As both ends of the 

 galvanometer circuit were connected with similarly situated Pt-Ag wires, the 

 magnitude of the thermo-electric effect having its origin in these contacts was 

 diminished. The Pt-Ag wires were further shielded by the massive casting of brass 

 which carried the contact maker. During all standardisations and experiments the 

 current through the bridge battery circuit was maintained at 0"013 ampere. 



Fig. 3 shows the general arrangement and the approximate resistance of the 

 various arms is indicated when the thermometers are at C., the resistances being 

 so arranged as to give nearly the maximum sensitiveness for a given current. 



The current through the thermometer coils was less than 0'006 ampere ; its heating 

 effect was so small that it could be disregarded, both thermometers and, therefore, 

 both blocks of metal being equally affected. 



The battery key was of the type described in ' Phil. Trans.,' vol. 184, p. 398, and 

 re-established the galvanometer circuit after the battery one was broken. Hence, the 



* The value of 8 was determined in the vapour of boiling aniline (184 -13 C.), as the resistance of 

 thermometer AA' in sulphur vapour would have exceeded the total range of our standard marble top box A. 

 The value of 6 was of secondary importance, as we were concerned only with the value of d6/dpt at vaiioiu 

 tank temperatures. 



VOL. CCXIH. A. 8 



