88 



INFRA-RED REFLECTION SPECTRA. 



at 9.2 to 9.3 ju, and a third band at 9.7 p. Curve a, fig. 76, gives the 

 reflection for a monochromatic red glass, No. 2745, made by Schott & 

 Co., of Jena ; curve b is for a plane parallel interferometer plate ; curve c 

 is for a piece of fluorescent uranium glass, while curve a, fig. 78, is for 

 a piece of ordinary plate glass. 



The fluorescent glass has an unusually low reflecting power. All of 

 the samples have a uniform reflecting power to 7.0 /*,, then a sudden 

 decrease, followed at 8 ju, by a large band of selective reflection. For 



FIG. 76. Glass. 



the transmission curve of glass (fig. 53) it will be noticed that there is a 

 decrease in the transparency beyond 15 p. Hence one would expect to 

 find the reflection curve to be irregular as observed, being abnormally 

 high just beyond the reflection band at 9.3 p., and abnormally low on 

 approaching the second large absorptive band which lies beyond 15/x. 

 The glass plates were from 3 to 8 mm. thick, hence opaque beyond 4 /x, 

 so that the reflection values are not influenced by energy reflected from 

 the second surface, i. e., the reflection is from only one surface. 



