p. LECOMTE DU NOtJY 749 



K being a constant (function of the resistance of the constantan 

 strip) of the instrument, calculated and experimentally checked, 

 equal to 0.21, we measured a current of 0.0028 amperes; this gives: 



0.21 X (0.0028)^ ; ^^^ = 0.00000165 



sec. 0.1 sq. cm. 



as 0.2388 cal. gr. = 1 watt sec, it corresponds to 0.000694 watts 

 by sq. cm. 



Correction for Equatorial Radiation. — This corresponds to the homo- 

 geneous radiation of a punctual source of energy of 87 watts; that is, 

 it would require 87 watts from a punctual source to radiate spheri- 

 cally in all directions an amount of energy of that magnitude. We 

 have measured this amount equatorially, that is, normally to a line 

 normal to the glower itself, and, of course, in the best conditions 

 of radiation. But as the beam of light assumes a greater deviation 

 from the equatorial plane, in the case of an incandescent rod, in other 

 words, as the square centimeter exposed to the rays stands higher 

 in latitude on the sphere, the amount of energy radiated is decreased, 

 since the rays are no longer emitted perpendicularly by the rod. 

 Around the two poles, there is even a region where there is no 

 radiation at all. The result is that, whereas the source acts as 

 radiating 87 watts equatorially, it radiates much less as soon as we 

 reach higher latitudes, and becomes zero at the poles, and the mean 

 value of the radiation is much less than 87 watts. It is known that by 



TV 



multiplying the energy radiated equatorially by ~, the real value 



of the radiating energy from the source is known. In this case, 



87 X - = 68.3 watts. 

 4 



Hence, out of the 92 watts sent into the filament, only 68.3 are 



radiated, and 23.7 are lost by convection and conduction. The 



92 , . 



ratio = 1.35 is in excellent agreement with the figure given by 



Lux: 1.34. 



This figure may be checked in another way: the input in the filament being 



4 

 91.8 watts, roughly 92 watts, it will radiate equatorially 92 X - = 118 watts, 



