20 Mr. Jx. H. M. Bosanquet on a new Form of Polar iscope, 



a material system," that we give a complete dynamical expla- 

 nation of that phenomenon. If Isomerism depends on changes 

 of potential energy, we must remember, to quote Prof. Clerk 

 Maxwell (Treatise on Heat, p. 283, 1st edit.), " that potential 

 energy depends essentially on the relative positions of the 

 parts of the system in which it exists, and that potential energy 

 cannot be transformed in any way without some change of the 

 relative position of those parts." 



Hence I think that the energy theory of isomerism is not 

 altogether inconsistent with the position-theory, and that both 

 meet with their fullest development in terms of the molecular 

 theory of matter. 



43. I have thus attempted to show that our ordinary che- 

 mical notation is founded on facts, that it gathers together and 

 symbolizes a great many phenomena, that it does not neces- 

 sarily imply the acceptance of any theory as to the constitu- 

 tion of matter, but that it receives its fullest meaning when 

 viewed in the light of the molecular theory. I have further 

 briefly endeavoured to point out some of the deficiencies of 

 chemical notation, but have expressed a belief that when the 

 present system is superseded by a better, the new will be the 

 legitimate outcome of, and will not be in any fundamental 

 point opposed to the old. 



II. On a new Form of Polariscope, and its application to the 

 observation of the Sky. By E. H. M. Bosanquet, Fellow of 

 St. Johns College, Oxford*. 



THE observation of faint traces of polarization, such as 

 present themselves in certain atmospheric and other phe- 

 nomena, requires polariscopes of great sensibility. The instru- 

 ment hitherto principally employed for the purpose is the po- 

 lariscope of Savart, formed of two similar plates of quartz, cut 

 at an angle of 45° with the axis, and superposed with the prin- 

 cipal sections at right angles. The appearance presented by 

 polarized light in this instrument, when properly arranged, con- 

 sists of a number of coloured bands with black or white centre ; 

 and its sensitiveness depends on the fact that these bands can 

 be recognized even when very faint, on account of the marked 

 character of the pattern they form in the field of view. In one 

 respect, however, this instrument possesses properties which 

 are not always advantageous. First, it is necessary that the 

 principal section of the analyzer between the plates and the 

 eye should be either parallel or at right angles to the direction 



* Read before the Ashmolean Society, Oxford, May 25, 1876, and com- 

 municated by the Author on behalf of the Society. 



