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



projected on such a screen a solar spectrum showing the fixed 

 lines for a great distance above H. 



The fluorescence excited by rays about and above H does not, 

 however, seem to suffer any change in intensity, but yields a 

 uniform and brilliant green light, on which the solar lines are 

 seen with admirable distinctness. Indeed this substance seems 

 to me to surpass any heretofore known as a screen for the study 

 of the violet and extra-violet rays. 



Thallene in Solution. 



As had been already noticed, thallene is soluble in a number 

 of liquids ; and in all cases it communicates a strong blue fluor- 

 escence to the solvent, or, more strictly, fluoresces strongly with 

 a blue colour in solution. 



When this blue fluorescent light is examined with the spec- 

 troscope, it is found, like the green fluorescence of the solid, to 

 break up into bands ; but in the solution these are found in all 

 cases to be displaced strongly towards the upper end of the spec- 

 trum, which at once explains the change of general tint in the 

 light from green to blue. 



Fig. 8, which represents the spectrum of the solution in ben- 

 zole, will, by comparison with fig. 5, indicate this change ; and 

 we shall see that the three most distinct bright bands at 6*8, 8*4, 

 and 9'8 in the spectrum of the solid are moved to 7*2, 8*9, and 

 10*7 respectively in the spectrum of the solution. 



If in place of benzole we employ chloroform as a solvent, we 

 find that the bands occupy sensibly the same positions ; but if 

 sulpuric ether is used, the bands are somewhat more displaced. 

 With turpentine the displacement seems to be a little less than 

 with ether, and with alcohol about the same, while with olive- 

 oil an intermediate position is occupied, and with carbon-bisul- 

 phide the displacement is least of all. 



The following Table will give some measurements of the po- 

 sitions of corresponding bands in various solutions : — 



Carbon- Benzole and Ar ., m 



bisulphide. chloroform. 01lve -° lL Turpentine. 



68-0 71-6 72-9 729 



87-6 88-5 89-6 898 



106-6 107-8 109-2 108'1 



Ether. 



73-8 

 90-1 



