94 Dr. H. Morton on the Fluorescent Relations of certain 





V 



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In this we find a very strong narrow band having the line F 

 in its centre, then a less-defined double band at 100 and 110 of 

 the scale ; another, yet less sharply defined, from 120 to 130 

 connected by a shade with the point about 140, where the ab- 

 sorption becomes total. The marked difference between this 

 and the absorption-spectrum of commercial anthracene consists 

 in the double character of the second band, and in the much 

 lower position of the third band, which ends, above, about where 

 that of the anthracene begins. 



We will now pass to the method of observation indicated 

 already in fig. 4. 



The screen upon which the pure solar spectrum was thrown, 

 located at E (see fig. 4), was prepared as follows : — A piece of 

 filter-paper was coated with pure thallene by rubbing it on in 

 powder with the finger. It adheres very well to the paper, and 

 produces in this way a very regular and beautiful surface. 



A strip of this is attached with gum to a piece of white card ; 

 and this slides in horizontal grooves in a frame E (fig. 3), which 

 is pierced by a large opening. 



The spectrum is so adjusted as to fall on the fluorescent strip, 

 and also on the adjacent part of the card; and we have the ap- 



Fig. 7. 



1 Q- . 2 4. 6 



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8 , 20 22 24 



f i 1 1 

 iiiiliiiiiinilii 



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HnBHniH 



\r 



-mi 







JXIMHHHI 



1 '.'fl 



A <* BC 1 



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i i 7 1 f a * ' Jin* 



pearance indicated in fig. 7, where S T represents the part of the 

 spectrum which falls on the thallene-covered paper, and R V that 

 portion which falls on the card. The spectrum upon the card 

 runs, of course, from red to violet, but even below the fixed 

 line G becomes very dim, and between G and H ceases to show 

 any decided light. Where these higher rays fall upon the 



