BELL. 



ULTRAVIOLET COMPONENT IN ARTIFICIAL LIGHT. 



19 



courtesy of the Director, this part of the work was clone in the Rogers 

 Laboratory of Physics where the conditions for getting natural light 

 were good. In Figure 5, A is a porte lumicre receiving the light from 

 the sun and forming by means of the iris diaphragm B, stopped to 

 3 mm. diameter, an image of the sun on the thermopile front at C, 

 before which was placed the usual quartz cell D. The thermopile 

 was connected with the galvanometer F, read by the telescope and 

 scale G. By the use of the diaphragm, forming a species of "pin 

 hole" image on the face of the thermopile, at a distance of 3 meters, 



-MW/ywvT 



(b 



Figure 5. Apparatus for solar radiation. 



the light and energy were cut down so as to be readable with compara- 

 tive ease. 



To measure the intensity of the illumination a Simmance-Abady 

 flicker photometer H was set up close alongside the thermopile so 

 that the solar image could be ciuickly moved so as to fall squarely 

 on the photometer disc. On the other side of the photometer at I 

 was an 80 watt tantalum lamp which was previously calibrated, in 

 terms of the current flowing through it, against a standardized Gem 

 lamp. From the source of supply the current was taken to this lamp 

 through an adjustable rheostat J and a mil-amperemeter K. In 

 measuring the light-intensity of the beam which was allowed to fall 

 on the thermopile, it was simply shifted from the face of the thermo- 

 pile to the face of the photometer and by means of the rheostat J 



