CAPACITY Foi; IIKAT OF MKTAI.S AT IMFFKKKNT TKMPKIIATMJKS. 



135 



t lie i-mls i .f tin- liriiting roil I!' was lial.'inrril a^iinst tliat \' :i mi!iilT <>(' <-:i<liiiimn 



cells, as in the ordinary method of experiment. 



Tin- siTuinl nlisiT\ IT inr.-isiin-il tin- [Hitrntiiil dill'Ti-iK'c ;il tln-i-iids of tin- :; olmi 

 coil, by means of a Thomson-Varley potentiometer (P), the readings being taken to 

 about 1 part in 50,000, by interpolation by galvanometer swings. 



Jin 



R'. 

 W. 



P. 

 S and 8'. 



B. 

 Cd. 

 GI. 

 Gj. 



Fig. 5. 



Heating coil in metal block. 



Manganin coil (about 3 ohm) immersed in oil. 



Thomson- Varley potentiometer. 



Rheostats to adjust current. 



Main storage battery. 



Standard cells balanced at ends of R'. 



High-resistance galvanometer. 



Paschen galvanometer. 



Observations were taken when the potential difference at the ends of the heating 

 coil was varied in steps from that of three to eight standard cadmium cells. The 

 temperature of the block was maintained approximately constant by cooling with the 

 ether tube. 



Calculation o 



If to is the resistance of the 3-ohm coil, W, and the current in the circuit is caused by 

 a potential difference of nE at the ends of the heating coil, and R' is the resistance 



