202 



MR. W. F. G. SWANN ON THE SPECIFIC HEATS OF AIR AND 



Fig. 2. 



To ends of heating coil 



The larger rates of flow amounted to about 0'5 litre per second, for, unless the rate 

 of flow is fairly large, the heat loss, which depends upon the temperature rise and not 

 upon the flow, forms an appreciable percentage of the whole energy supplied. 



(3) Measurement of the Electrical Energy. The electric current was supplied by 

 four large accumulators. It passed through a rheostat, the heating coil of the 



calorimeter, and a standard resistance coil 

 which will be referred to as the secondary 

 standard. If E! and E 2 are the potential 

 differences between the ends of the heating coil 

 and standard resistance coil respectively, and if 

 R is the resistance of the standard, the electric 

 energy supplied to the heating coil per second 











o 



IS Kj-L&zjK,. 



EI and E 2 were measured in terms of the 

 cadmium cell, on a four-dial potentiometer. 

 The potential differences between the ends of 

 either the heating coil, standard coil, or 

 cadmium cells could be balanced on the poten- 

 tiometer by bringing the leads to six mercury cups, cut in a paraffin block in the 

 manner indicated in fig. 3. 



