METALS. 



305 



plate is cumulative, and one would have dark lines superposed upon 

 a dark background, just as Abney and Festing' found for their absorp- 

 tion spectra at i fi. 



Carbon Arc. 



In figure 137 is given the emission spectrum of the carbon electrodes, 

 curve a, and that of the violet vapor of the arc, curve h. It will be 

 noticed that there is but little radiation from the vapor except 

 a slight amount from 2 to 3 /x. On the other hand the deflection was 

 thrown off the scale for the radiation from the electrodes, just beyond 

 the red. Snow (loc. cit.) found the radiation from the arc vapors con- 



10 



a 



7 



<Ji 6 



% 

 0) ^ 



3 4 



Fig. 137. 



7^ 



centrated in a single line, in the violet, at 0.385 /x. This line is four 

 times as intense as the one at i .09 /a. In the present work the lines are 

 of about equal intensity, due in part to the loss of intensity of the violet 

 line, caused by the radiometer window. A new line occurs at 1.2 /x, 

 while on a thorough re-examination no line was found at 4.52 /x. This 

 is of considerable interest, since it shows that no COo is formed, and 

 that the electrodes are consumed in a different manner. They do not 

 disappear in the ordinary form of combustion. There is but little resi- 

 due from mechanical disintegration ; they disappear chiefly in the form 

 of vapor. The absence of radiation from the carbon vapors is in 



^Abney & Festing, Phil. Trans., 177, p. 



