Physical Constants of Thallium. 



197 



examining the thermo electric power of two metals, I twisted 

 together their ends and coiled the joint round the bulb of a 

 thermometer, immersing the whole in a bath of olive oil. 

 The other junction was kept in a large beaker of cold water 

 with a thermometer in it, which was observed from time to 

 time, and if necessary, correction made for the rise of 

 temperature. Tliis rise was never more than a degree, the 

 corresponding correction being one or two scale divisions. 

 The relation between the observed values of temperature and 

 galvanometer reading is parabolic, and if we express the 

 excess of the temperature of the hot junction over the cold 

 by t, and the number of scale divisions by s, then s z= a t -\- 

 h t^ is the connection between .s and t, where a and b are 

 constants to be determined preferably by the method of least 

 squares, as was done with each set of observations, though 

 the operation is rather laborious. The following table may 

 be taken as typical of the accuracy attained : — 



In this case, the metals being thallium and lead, the 

 resistance of the circuit was 1-395 ohm. The equatioji to 

 the parabola, represented by the first and second columns, 

 is s = 2-36^ - 00.512 t^ where t = T ~ 19. A Daniell 

 cell, when used to charge a condenser, gave a throw of 

 276-3 sc. clivs.; a Latimer Clark cell gave 846-4- ; the E.M.F. 

 of the Daniell is thus— 1-435 x 276-3 -^ 346-4 = 1-144. 



