922 Transactions of the American Institute. 



As a rule, however, the fluorescent light yields the same spectrum, 

 with any rays that are capable of exciting it. 



While there exists the remarkable similarity between the fluores- 

 cent properties of chrysogen and thallene which are evident on 

 inspection of Plate III, yet we must not fail to notice the following : 

 The fluorescent spectrum of thallene wants the lowermost division 

 of what corresponds with the first and second bright bands of chryso- 

 gen, this portion being, with it, all one broad band. 



On the other hand, there is in the spectrum of thallene a band, very 

 faint, indeed, but yet distinguishable, if a violet glass is added to 

 the copper tank (see Fig. 1). This band, though not shown in No. 1 

 of Plate III, exists at about ten of the scale, but the corresponding 

 displaced band, is seen much more plainly in the solarized thallene, 

 and is shown in No. 3 of Plate III. 



In the next place, in exposure to sunlight, the chrysogen is entirely 

 decomposed, or, at all events, ceases to give any bands of fluorescence, 

 while, as we have seen, the thallene, while losing its yellow color, 

 only has its fluorescent spectrum displaced. 



Again, the absorption band, between ten and eleven in thallene, is 

 a decidedly double one, while that which corresponds to it in chryso- 

 gen is single. 



These, combined with marked differences in their boiling points 

 and solubilities, serve, we think, to establish the individuality of the 

 new body. 



April 5, 1872. 



Prof. S. D. Tillman in the chair; Kobert Weir, Esq., Secretary. 

 The chairman opened the meeting by reading the following paper : 



ON THE TRANSMISSION OF HEAT. 

 By Samuel D. Tillman,- LL.D. 

 The uses to which heat is applied in the arts are so nun e • us and 

 important that methods for its more economical generation and trans- 

 mission are always examined with interest, more especially since 

 science has demonstrated that, with the best contrivances yet employed, 

 but a small portion of the actual heat product of combustion has been 

 converted into available power. Our subject will be best illustrated by 

 + reating it under different heads. 



