BELL. — ULTRAVIOLET COMPONENT IN ARTIFICIAL LIGHT. 



These were firmly clamped in the binding posts of the instrument by 

 working through the side tube attached for the reception of the quartz 

 window. The thermopile was then pushed up exactly opposite the 

 side tube and wedged in place with cork and cotton wool attached 

 with shellac. The end of the side tube was flanged out and ground 

 flat for the fitting of the quartz window and after the shellac had dried 

 out thoroughly the window was fastened in place and the lower end 

 of the tube drawn out for the attachment of the pump. The tube 

 was pumped to the high vacuum usual in an X-ray tube, and was then 

 sealed. It was mounted as shown in a block of wood to which was 

 secured the disconnecting terminal, reached by a long handled plug, 



Figure 1. Vacuum thermopile. 



Figure 2. Quartz cell. 



and the whole was then surrounded by a pasteboard case having a 

 hole just opposite the quartz window, and packed full with loose 

 cotton wool. The galvanometer was of the D'iVrsonval type, having 

 a sensibility of 2 X 10"** ampere per mm. scale deflection. Its period 

 for the attainment of a complete deflection, was, under the ordinary 

 conditions of its use, 1 minute. 



The galvanometer deflections were read by a scale and telescope, 

 the scale being a special one bent to 1 .5 meters radius. The thermo- 

 pile indications were calibrated in absolute measure by observations 



