1911] on Recent Experiments ivith Invisible Light. ini 



I can show you a photograph of the shadow cast by a flame of this 

 description, and you will observe that the shadow is blackest at the 

 point where the flame is brightest, that is, at the point where the 

 minute carbon particles, which, by their incandescence, cause the 

 luminosity, are being set free from the hydrocarbon vapour. 



There are other questions which can doubtless be investigated to 

 advantage by means of ultra-violet photography. It is well known, 

 for example, that the amount of ultra-violet light emitted by a body 

 increases with the temperature. By photographing groups of stars 

 through the quartz silver filter, and comparing the photometric 

 intensities of the images obtained in this way with the intensities 

 as shown on a plate made by means of yellow light, valuable data 

 might be obtained. This method is merely an extension of one 

 already in use at the Harvard Observatorv. 



[R. W. W.] 



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