378 ROMBERG. 



the Jefferson' Physical Laboratory of Harvard University, and to 

 Professor Davis is also due the distinctive feature of the method, as 

 will be pointed out below. 



The method may be explained schematically by reference to the 

 diagram, figure 2. Hot water flows through a tube Fi containing 

 resistance thermometers Ti and T'l, the tube being in thermal contact 

 at C between these two points, with another similar system F2, in 

 which cold water is flowing. The two streams of water are made 

 equal. The thermal coupling C is variable; a device due to Professor 

 Davis, and of fundamental importance in giving the method its 

 advantage. 



7; 



WW 



r/Q. 2. 



With constant temperatures Ti, To, and flow/, readings are taken of 

 Ti—T\ or T'o—T2, and of (Ti— 7"i) — (T'o— T'a). This is repeated 

 for other values of the flow, and for other conditions of the thermal 

 coupling. 



If there are no complications, and if Ti— T\ is small, the ratio of 

 the specific heats is 



cj _ T'.- To 

 Co ~ 1\ - T\ 

 and therefore 



C2-C1 ^ iT,-T\) - jr.- To) ^ ^0 

 Co ~ 7'i- n ~Ai 



Heat currents to and from the flowing stream at places other than C 

 may introduce errors in the thermometer readings. These errors may 

 be represented as 



. ^ . _ -^JTi, T2) Depending upon the temperature variations 

 ^ f of the water-supply. 



o\ -) i — ^^^ ^^^^ ^^ cross-heat-losses proportional to the 



' / temperature differences T'l — 2"i and 2^2— T'2- 



i 



