PHYSICS NINETEENTH CENT.SPECTROSCOPY. 489 



the new substance, which proved to be a metal having chemical pro- 

 perties intermediate between those of lead and the alkaline metals. 

 For this metal Mr. Crookes proposed the appropriate name of thallium, 

 the Greek word Qa.XX.os, a green branch. Since Mr. Crooke's discovery 

 of thallium, the spectroscope has been the means of adding several 



