[LEVI] PHOTO-ELECTRIC CONDUCTIVITY OF DIAMOND 243 



4. Diamond No. 4 was triangular in shape, of side 8 mms. and 

 of 1 mm. thickness. It was distinctly coloured, with a brownish tinge, 

 and was a transparent, natural crystal. 



5. Diamond No. 5 was a very clear, natural crystal, about 6 by 

 4 by 1 mms. with a triangular etch figure on one of its faces. 



6. Diamond No. 6, about 5 by 5 by 1 mms., was a natural 

 crystal, nearly opaque, with a surface of granular appearance. 



7. Small crystals of willemite for examination were broken ofï 

 from a large sample which came from Franklin, New Jersey. The 

 mineral was of a pale green colour and quite opaque. 



8. The crystals of kunzite used were loaned to Prof. McLennan 

 through the kindness of Dr. Kuntz, of Messrs. Tiffany, New York. 

 The mineral was of a pale purple colour and semi-transparent. 



(b) Spectral Absorption. 



The photographs shown in Plate 1, Fig. 1 were obtained with a 

 quartz spectrograph, using a mercury arc in quartz as a source of 

 light and interposing each crystal in succession between the source of 

 light and the slit of the spectrograph. It is seen that diamonds Nos. 

 3, 4, and 5, although more transparent in the visible, were opaque to 

 radiation in the ultra-violet of shorter wave-length than X = 2967 A, 

 while diamonds No. 1 and No. 2 were the only crystals transparent 

 down to X = 2000 A. 



Thermopile measurements of the energy from the carbon arc 

 were made with diamond No. 1 interposed between the source of 

 light and the slit of the spectrograph. By comparing these with 

 measurements made when the diamond was removed, data for the 

 curve in Fig. 1 were obtained. From this curve, in which per cent, 

 absorption was plotted against .wave-length, it is seen that diamond 

 No. 1 showed rapidly falling absorption with decreasing wave-length. 



(f) Fluorescence and Phosphorescence. 



The fluorescing and phosphorescing properties of the crystals 

 were observed under the influence of gamma rays. It was found 

 that all the diamonds showed a bluish luminosity, the cut edges of 

 diamond No. 3 being particularly bright. It was also noticed that 

 willemite glowed a bright green and kunzite a dull red under the 

 gamma rays. On removing the source of radiation, the luminosity 

 of all the crystals vanished, except that of diamond No. 1, which 

 continued to glow for many minutes. These characteristics are 

 illustrated in the photographs in Plate 1, Fig. 2. 



