536 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



from the arc spectrum, are present in the Wehnelt, but with less inten. 

 sity, and are not decreased proportionately. 



2. These two lines, X 4911.0 and A. 4924.0, belong to a class which 

 will be referred to again under tin and lead, broad and diffuse, and dis- 

 tinctly different from the other lines of the spark in appearance. The 

 position of these lines in Kayser and Runge's series * has not been de- 

 termined, and the question as to whether they belong to the same class 

 as the tin lines noticed by Crew f is still an open one. 



3. The marked underlying band spectrum. This is so faint as to be 

 difficult of reproduction, though a large part of it may be measured, 

 especially the brighter band from X 4163.0 to A 4257.0. Here 19 

 maxima are visible, but it is in many cases difficult to decide whether 

 lines or the heads of flutings are being measured. This band spectrum 

 seems to be characteristic of this method of producing a spectrum, and 

 the author knows of no other notices or measurements of it. 



MERCURY. [Plate 3, Fig. 11.] 



Spark. Amalgamated copper terminals. 



Arc. Metallic mercury on carbon electrodes. 



Wehnelt. Platinum point in solution of mercuric nitrate. 



* Vid. W. A., 43, 395 (1894). 



t Astropliys. J., 12, 107 (1900). 



