Intelligence and Miscellaneous Articles, 



471 



II. Series. 



Strength of Total 



current. radiation. 



48-0 

 76-2 

 94-2 



102-0 

 254-0 

 3920 



Optical 



radiation in 



candles. 



0-3 



5-5 



24-0 



Both series show very clearly how enormously the emission of 

 light increases with increasing temperature. 



The following considerations show that there is a simple relation 

 between strength of current and total emission. The thermal 

 equilibrium of the lamp is defined for each strength of current 

 by the fact that the quantity of heat produced by the current in 

 the lamp is equal to that given out. Hence for each strength of 

 current J the following relation holds — 



P¥=C . S, 

 where 



W is the resistance of the carbon filament at the temperature in 

 question ; 



S the radiant energy sent out by the lamp ; and 



C a constant. 



From the above equation we get 



™=c. 



If W, the resistance of the carbon filament for the temperatures 

 here in question (900-1500°), were constant, the quotient must be 

 a constant, 



P 

 S' 



The following values are obtained for these quotients for the 

 strengths of currents : — 



J 44-5 48-8 57-0 67'0 75-0 88-2 48-0 76-2 94-2 



J 2 /S... 22-8 24-5 20-7 23-0 22'5 22-4 22-6 22-8 22-6 



Such deviations as occur in two experiments are to be ascribed 

 to variations in the current which occur during the observation of 

 the total radiation. It follows, therefore, from the table that the 

 resistance of the carbon filament from about red heat to white 

 heat is, so to speak, independent of the temperature. This seems 

 to be the case for the coefficient of absorption of the glass globe 

 of the lamp. I may take the opportunity of remarking that ordi- 



