TROWBRIDGE. SPECTRA AT HIGH TEMPERATURES. 687 



the quartz tubes the light from the tubes was very feeble, traces of 

 metallic spectra appeared, and the walls of the quartz capillaries were 

 speedily covered with thin films of the metals ; even at the first dis- 

 charge, before there was a sensible obscuration due to the formation of 

 the films, there was no evidence of gaseous spectra. The main discharge 

 appeared to be carried over by the metallic vapor and no dissociation 

 of the gas was evident. 



Measured by definite amounts of electrical energy, the rating of the 

 intensity of spectral lines differs totally from existing eye estimates. 

 The lines which coincide with the II. II. lines in the spectra of the metals 

 with high melting points generally came out first on the photographic 

 plate when the method of successive discharges was employed. 



Rarefied nitrogen gave far less light than hydrogen, water vapor, or 

 oxygen. When oxygen was employed, characteristic groups of doublets 

 were obtained like the A and B groups in the solar spectrum. The 

 heads of these groups apparently coincided with the middle of broad 

 lines shown in Figure 4. The middle of these broad bands or broad 

 lines coincides also with narrow lines usually attributed to silicon. Are 

 certain lines attributed to silicon really oxygen lines ? Salet, and also 

 Rowland, assign the photometric intensity of 4 to the lines 4131.5 and 

 41 26.5, 3 to the lines 3905 to 3855. 7, and 10 to the line 2881. When the 

 lines given on plate 4 and those on plate 7 are photographed on the same 

 plate by the same number of discharges and are compared in regard to 

 intensity, the rating is completely reversed, the lines at 4131.5 and 4126.5 

 and 3905 to 3855.7 being 10, and the line 2881 being three or four. 



The broadening of what have been considered metallic lines in rarefied 

 cases I consider a most interesting phenomenon. Only the strong lines 

 of the spark spectrum of the metal in air seem to be reversed under the 

 effect of powerful discharges in rarefied gases. This broadening appears 

 to be the evidence of reactions between the vapor of the metal and the 

 surrounding gases. In this connection it is well to bear in mind the fact 

 that metals continue to give off gases for a long time when submitted to 

 powerful electrical discharges in vacuum tubes. This has been shown 

 by Dr. Rollins of Boston in his researches on X-rays. 



These nascent gases are in condition to exhibit complicated reactions 

 with the strongly heated metallic terminals. 



My experiments lead me to strongly doubt conclusions drawn from 

 the apparent absence of this or that element in the spectra of stars ; for 

 there is a strong possibility that reactions enter which may mask the 

 presence of this gas or that metal. 



