482 Royal Society : — 



also to be derivable from the principles stated in §§ 9 and 16 ; as B 

 being dependent on d 2 , must change proportionally to the square of 

 molecular condensation (see § 16). 



§ 19. In consequence of § 9, the lines of Fraunhofer (although the 

 constancy of the lengths of undulation, to which they answer, remains 

 unaltered), when refracting substances are condensed, must advance 

 their centre toward the violet end, in analogy to the phenomena of 

 absorption, observed by Weiss (Poggendorif's 'Annalen,' 1861). For 

 this reason absorption must depend on the length of the undulation. 



These propositions, and some others of similar nature which I suc- 

 ceeded in deriving, incomplete as they still may be in many respects, 

 prove at all events that, even in this department of human knowledge, 

 theoretical points of departure exist from which, by progressive 

 investigation, the real connexion of facts may possibly be traced. 

 My next purpose is to coordinate as much as possible whatever is at 

 present known of facts, bringing them under general points of view 

 as materials for a future scientific theory. I intend to publish by 

 and by these investigations as completely as possible, in constant 

 connexion with the phenomena which they are suited to explain, 

 never leaving the secure foundation of experimental research. 



Here I intend only to offer a brief abstract of the facts obtained 

 through the first two series of investigations, published in the * Pro- 

 ceedings ' of the Vienna Imperial Academy (vols. xli. and xlii.). 



These investigations took place in the Imperial Physical Institute 

 of Vienna, and could only be effectually accomplished through the 

 liberal and kind assistance I received from the Director of the Insti- 

 tute, from the Director of the Imperial Museum of Mineralogy, and 

 from the Superintendent of the Chemical Laboratory of the Imperial 

 Geological Institute. 



In these results are comprised — the exponent of refraction, the 

 calculated axial angle, the aperture of the cone of internal conical 

 refraction, the measure of the apparent axial angle, and crystallogra- 

 phical investigations. 



For brevity's sake I will only communicate the exponent of refrac- 

 tion for Fraunhofer' s lines B and H, and the most important among 

 the crystallographical determinations. 



1. Diamond. C. 



^ B = 2'46062 / y H =2-51425 



2. Mellite. A1 2 3 , 3C 4 3 +18HO. 



w B =l*53450 e B =l-50785 



Wh =1-56113 €H =l-52769 



3. Acetate of Ammonia and Oxide of Uranium. 



[AmO, A+ 2(Ur 2 3 , A) + 6 HO.] Pyramidal. 

 u> =1-4/538 e B =l'48770 



WH =l-50687 £ h =1-51974 



