PoLLOK — The Vacuum Tube Spectra of sows Metallic Vapours. 211 



bands develop with great freedom, especially when no condenser is used. The 

 vapours of mercuric and mercurous chloride, so far as examined, appear to give 

 rise to the same lines as metallic mercury when under the same condition ; the 

 bands seen on the plate are mostly due to nitrogen accidentally present. The 

 ultimate line of mercury is A2536'7 and not X 2534-9, as given in my short 

 table in the paper on " Index of the Principal Lines of the Spark-Spectra 

 of the Elements."! 



The same line is evidently tlie ultimate line in the vacuum tube spectrum, 

 both with and without the condenser. The lines A 2847-9 and X 2225-7 show 

 with the condenser, but not without it, in the case of both metal and chloride. 



Principal Lines of Mercury. 



1 Proc. Royal Dublin Society, vol. xi., p. 214, 1907. 



2i2 



