88 Professor Deivar [April 1, 



pose that more volatile metals would give their lines too. Linings 

 of thin sheet copj^er, lead, cadmium, zinc, aluminium, and tin were 

 successively j)ut into the tube, and their effects on the flash observed. 

 Copper gave one strong line in the green (wave-length 5104: "9), but 

 no other line in the visible part of the sjDectrum. In the ultra-violet 

 two strong lines between Q and R came out in the photographs, fre- 

 quently as reversed lines. Some of the photographs showed also 

 something of the shaded bands in the blue which are ascribed to the 

 oxide of copper. The green line of copj^er had been observed in the 

 flash before the cojDper lining was put into the tube ; and we con- 

 cluded that the cojDjjer was derived from the brass with which the 

 small lateral tubes were fastened into the large tube, or that the iron 

 of the tube contained a little copper. When the leaden lining was 

 used, only one visible line of lead was developed, and that was the 

 strong violet line, but two ultra-violet lines between M and N were 

 strongly depicted on the photographic plates. The violet line of 

 lead had also been observed in many of the photograjDhs taken before 

 the leaden lining was introduced. This we ascribed to the leaden 

 washers used to make the glass or quartz plates air-tight. The line 

 was greatly increased in strength by the leaden lining. The zinc 

 lining gave no visible line at all, notwithstanding the easy volatility 

 of the metal ; and in the ultra-violet it gave only a very doubtful 

 impression of one of the lines near P. The cadmium, aluminium, 

 and tin linings gave no lines at all. Zinc dust put into the tube 

 gave no zinc lines, merely increased the continuous spectrum, and 

 speedily rendered the quartz end opaque. 



A clean wire of magnesium put into the tube gave the h group of 

 lines, but no other line. No trace of the blue lino, so conspicuous in 

 the flame of burning magnesium, nor of the triplets near L and S, 

 nor of the very strong line, the strongest of all in the arc, at wave- 

 length 2852. b^ and bn were well seen ; but as b^ is an iron line, as 

 well as a magnesium line, and the iron line was visible in the flash 

 before the magnesium wire was introduced, we cannot be sure whether 

 the magnesium line, as well as the iron line, was present in the flash. 

 Magnesia did not develop any line at all; merely augmented the 

 continuous spectrum. 



Compounds of sodium, such as the carbonate and chloride, intro- 

 duced in powder gave the ultra-violet line between P and Q strongly, 

 frequently reversed ; but no other line except of course D. Potassium 

 compounds developed, often reversed, the pair of violet lines, and also 

 the ultra-violet pair near O, but no others. 



A strip of silver developed two ultra-violet lines, one on either 

 side of P ; but we could not detect in the flash the well-known green 

 lines of that metal. When powder of silver oxalate was introduced, 

 the yellowish- green line (w.l. 5464:) was seen at the first explosion 

 but not afterwards. As silver oxalate is itself an explosive compound, 

 decomposing with an evolution of heat, it is reasonable to ascribe the 

 appearance of this line at the first explosion to the extra temperature 

 so engendered. 



