Fluorescence produced by Ultra- Schumann Rays. 457 



radiation exciting one of the nitrogen bands of shorter wave- 

 length which was being transmitted. In all the photographs 

 of long exposure when purified nitrogen was used, there is 

 also a fluorescence at about 2300 A.U. The radiation exciting 

 this fluorescence is not very strongly absorbed by either quartz 

 or fluorite. Exposures made to detect a possible transmission 

 of any of the radiation exciting fluorescence through laminae 

 of fused quartz and thin films of mica gave entirely negative 

 results. 



If the radiation from the spark which has been studied in 

 this paper is really of the nature of light, then it should be 

 possible to refract it by passing it through the thin edge of 

 a prism of quartz or fluorite. A quartz prism ground to a 

 razor edge by Petitdidier was accordingly placed in the appa- 

 ratus in such a way that the radiations passed through the 

 very edge of the prism. The edge of the prism was pressed 

 against a piece of black paper to prevent any of the radiation 

 from passing by without going through the quartz. For 

 this experiment the original jet-apparatus (fig. 1) was used, 

 mounted in inverted fashion and adapted to the present work. 

 A tube was provided to feed the nitrogen from the rear 

 (similar to the tube T, fig. 2). The arrangement of the spark, 

 slit S, prism Pr, bedplate A', and tube T viewed end-on, is 

 shown in the sectional diagram fig. 3 in the text, which is 

 drawn as seen from the direction of the spectroscope. 



Fisr. 3. 



Passing a current of purified nitrogen of about one-third 

 litre per minute into the jet-chamber and exposing for an 

 hour and a quarter, cleaning the prism frequently, the ex- 

 posure of fig. 9 was obtained. This photograph shows in 

 the first place that the radiations here being studied are 

 refracted. Further, since the fluorescent streamer is fairly 

 broad, it indicates that for an extremely thin refracting edge 



