RECENT PROGRESS IN CRYSTALLOGRAPHY 97 



two series with coloured flames, but it has also enabled deter- 

 minations to be made of the exact wave-lengths for which many 

 interesting special phenomena occur, in which this research 

 has been rich. It is essentially a compact spectroscope, con- 



FlG. I. 



structed to transmit as much as possible of the light which 

 streams from the condenser of an electric lantern, and with 

 the observing eyepiece replaced by a second slit, although the 

 eyepiece can be readily attached for calibration purposes. A 



7 



