166 



Capt. Abney and Col. Festing. 



[June 19, 



sconce lamps as measured by the thermopile is very small com- 

 pared with that of the dark rays, in fact is almost negligible, and 

 from fig. 2 it will be seen that after a very few watts of electrical 

 energy, the intensities of the rays which radiate most energy increase 

 directly proportionally to the number of watts expended, and hence 

 that their integration is also directly proportional to the number of 

 watts expended. 



FIG. 4. 



Further for any slight deviation from the straight line in the most 

 refrangible rays there is a deviation in the opposite direction in the 

 rays of very low ref rangibility. These apparently counterbalance one 

 another, and hence we have the total radiation becoming a straight 

 line. 



It now becomes of interest to determine the thermogram of the 

 radiation for different electrical energies expended in the filament, 

 and such are given in fig. 4. 



