Thermoelectric Circuit of Three Metals. 



637 



Date 



Laboratory 



Resistance compensating E.M.F. 



Mar. 23. 



temperature-. 



of three Weston cells. 





7023 (a few minutes after com- 

 pletion of the circuit) rising 









to 7044. 



„ 24 



11° 



7050, 7051, 7049-5. 



„ 25 



11°-13° 



7051-5, 7050, 7051, 7051-5. 



„ 27 



ll°-5 



7053 and (after opening the circuit 

 for two hours) 7040. 



„ 28 



11° 



7052, 7053. 



„ 29 



10°-11° 



7052-3, 7052-0, 7052-4, 7051-5. 



„ 30 



11°-12° 



7048, 7047, 7046. 



„ 31 



12°-15° 



7047, 7046, 7045. 



Apr. 4 



10° 



7059-5. 



„ 5 



., 11 





7056. 

 7056. 



14° 



„ 12 



„ 13 





7049, 7051-5. 

 7051, 7052, 7051. 



15°-16° 



„ 14 



16° 



7052-5, 7052. 





13°-14° 



7056, 7057-5. 



Let W be the E.M.F. of the three "Weston cells (see § 2) and 

 let r be the value of the compensating resistance, so that W = ri. 



Let E be the E.M.F. of the ther mo-circuit, and let s be 

 the value of the compensating resistance. Let the current 



used in this case (approximately — — ) be represented by xi, 

 so that E=m. 



E is to be determined from the equation 

 E s 



W 



= x- 



where x is a fraction depending on the resistances of the 

 circuit of fig. 1. 



For the determination of x, Weston cell No. 3 was allowed 

 to produce a current in the manner already defined, and the 

 compensation apparatus was used to balance a definite fraction 

 of the E.M.F. of the cell, the current flowing through the 

 compensation apparatus being alternately i and xi. The 

 following specimen of the observations shows the order of 

 magnitudes involved : — 



Compensating 



resistance in ohois 



(large current). 



Compensating 



resistance in ohms 



(small current). 



70-62 

 70-61 

 70-61 



7058 

 7058 



x= -010004 



