PoLLOK — The Vacuum Tube Spectra of some Metallic Vapours. 209 



temperature at which I carried out the experiment. Bands developed 

 when no condenser was used, and there was an excess of vapour in the 

 tube, particularly with the vapour of the metal, and they show on the plate 

 from about X 4300 to X 4100. It is a noticeable fact that in the ease of zinc, 

 which gives some very characteristic lines in the arc spectrum, that do not 

 appear in the spark spectrum, not one of these lines shows with the vacuum 

 tube spectrum even faintly on the original plate, and those so marked were 

 carefully looked for. 



Principal Lines of Zinc. 



gCIENT. PROC. E.D.S., VOL. XIII,, NO. XV. 



2i 



