Determinina the Radiation Constant. 



271 



Consequently 



dT/dt=Aa{T 1 '-T), 



or 



dT 



A(T! 4 -T 4 ) ' dt 



w 



If the galvanometer readings were proportional to the 

 current existing at the instant of reading, we should have 

 dT/dt by simply noting successive deflexions at known times. 

 But, owing to the moment of inertia of the moving part of 

 the galvanometer and the viscous resistance, the reading will 

 not always indicate the current at the instant, as will be seen 

 from the investigation below^ (Appendix). In this case, 

 however, the readings did indicate the temperature, when 

 plotted to eliminate oscillations. 



The actual arrangement of the apparatus is shown 

 diagrammatically in fig. 1. A is a cylindrical vessel of 



15*3 cms. internal diameter : to the underneath side of this 

 vessel was soldered a polished copper hemisphere, indicated 



