4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8/ 



The two distributions of energy, adjusted for equality for visible 

 radiation measured as indicated, are shown in Figure 2. In order to 

 determine the distribution of energy in the chambers with and with- 

 out the heat-absorbing filters, a curve of relative emission per unit 

 wave length of radiation for a tungsten filament at the absolute tem- 

 perature of 2,980° K. was constructed. This tungsten radiation curve 

 was then corrected for energy absorbed by the pyrex filters and 

 1.5 cm of water. Another curve was obtained by further correcting 

 for energy absorbed by the heat-resisting, heat-absorbing light shade 

 filter (8 mm thick) and 1.5 cm of water. From each of these two 

 distribution curves corresponding response curves were drawn by 



Table i 

 Light sources and iutcnsittcs 



" p, pyrex; h, Corning heat-resisting, heat-absorbing, light shade filter, 8 mm thick. 

 * For these measurements a circular piece of Corning heat-resisting, heat-absorbing, dark 

 shade filter, 2.82 mm thick was placed over the Weston photronic cell. 



applying the factors obtained from the sensitivity curve of the 

 photronic cell with its special heat-absorbing filter. The ratio of 

 the areas under the two response curves then gave a factor which 

 was applied to one of the distribution curves in order to adjust 

 their relative values so as to yield equality of total response, that is, 

 equality of visible radiation as determined by the photronic cell with 

 its filter. These two adjusted curves are the ones presented in 

 Figure 2. A comparison of the areas of these curves shows that the 

 total energy applied to the plants receiving no near infra-red radia- 

 tion was 22 per cent of that applied to the plants receiving radiation 

 including the near infra-red. 



Thermometers were hung in the chambers in such a manner that 

 their bulbs were shaded from the direct rays of the lamps but were 



