Tube containing 

 Helium gas de- 

 rived from the 

 mineral Cleve- 

 landite. 



( Tube of Radium 

 J emanation, a 

 I year old. 



Tube of Hydro- 

 gen gas for 

 comparison. 



FIG. ii. 



Photographs of the "spark" spectra of A, Helium as extracted from 

 the mineral Clevelandite of B, the Radium "emanation" after a year's 

 enclosure in the tube used and of C of Hydrogen gas : copied from the 

 paper by Mr. F. Giesel in the Berichte der Dnitschen Chemischen Gesellschaft, 

 vol. xxxix, part 10. 



The three photographs are accurately super-imposed so as to show the 

 coincident lines. 



The spectrum B of the tube containing radium emanation is the one 

 which we are comparing with the other two. When the radium 

 emanation was first enclosed there was only a small quantity of helium 

 developed in it, but after keeping for a year the quantity has greatly 

 increased. After five minutes "sparking" (passage of the electric spark 

 through the tube) the chief lines of helium become evident but faint in 

 intensity. The present photograph B was obtained after forty minutes 

 sparking, and one result of that longer "sparking " has been that a minute 

 quantity of water vapour in the tube has been broken up so as to yield the 

 hydrogen spectrum, which is accordingly seen accompanying the now strong 

 and brightly developed helium spectrum. 



The lines of the spectrum B which correspond with those of hydrogen 

 are at once recognised by the juxtaposition (below) of the pure Hydrogen 

 spectrum from another tube C : the lines in B belonging to and indicating 

 helium are also recognised by comparison with the pure helium spectrum 

 of the tube A juxta-posed above. A very few of the lines in B must be due 

 to other minimal impurities as they are not present either in A or C. 



Thirteen lines of the helium spectrum are thus photographed and 

 recognised in the radium emanation. 



The following lines are present in the photographic but invisible 

 spectrum of radium (not given in fig. 10), viz. at 381-47 /*/* (the strongest 

 line in the radium spectrum) and at 364-96 (a strong line). 



In the photographic but invisible spectrum of helium there are three 

 very faint lines between wave-length 447-2 and 443-7 (appearing as two 

 only in our photograph); a moderately strong one at 438-8; others at 

 414-4, at 412-1, at 402-6, and 396-5 ; a very strong one is present at 388-9, 

 and a very faint one at 381-9. All these are seen in the photograph A and 

 also in B. Special treatment and spectroscopes reveal four other very 

 faint lines in the helium spectrum the one furthest in the invisible 

 direction [(that is of highest refrangibility and lowest wave-length) being 

 placed at 3186 (Soddy). 



G 2 



