30 Br. C. K. Akin on Calcescence. 



consists of three compartments, of which the median takes in 

 the visible rays, and the two others, respectively, the rays of 

 greater refrangibility and of less refrangibility than corresponds 

 to visible or light-rays. In order to avoid circumlocution, and 

 the ambiguity which attaches to the terms actually in use, it is 

 proposed to adopt in the sequel the following nomenclature for 

 the above-mentioned three classes of rays. The visible rays will 

 be called Newtonic, those of greater refrangibility Ritteric, and 

 finally those of smaller refrangibility Herschellic — the name 

 being formed in each case from that of the discoverer of the 

 particular class of rays. By means of this nomenclature it is 

 easy to give a complete list of the transmutations of rays a priori 

 possible, and which accordingly is here appended : — 



Transmutations. 



(1) Of Ritteric rays into Ritteric rays of less refrangibility. . 



(2) Of Ritteric rays into Newtonfc rays. 



(3) Of Ritteric rays into Herschellic rays. 



(4) Of Newtonic rays into Newtonic rays of less refrangibility. 



(5) Of Newtonic rays into Herschellic rays. 



(6) Of Herschellic rays into Herschellic rays of less refran- 



gibility. 



(7) Of Herschellic rays into Herschellic rays of greater re- 



frangibility. 



(8) Of Herschellic rays into Newtonic rays. 



(9) Of Herschellic rays into Ritteric rays. 



(10) Of Newtonic rays into Newtonic rays of greater refran- 



gibility. 



(11) Of Newtonic rays into Ritteric rays. 



(12) Of Ritteric rays into Ritteric rays of greater refran- 



gibility. 



4 Degradation and Elevation. — Of the enumerated twelve 

 species of transmutations, the phenomena of fluorescence and 

 phosphorescence afford only instances under (2) and (4); for, as 

 previously stated, these phenomena consist in an emission of 

 light, or Newtonic rays, consequent upon the incidence of either 

 Newtonic or Ritteric rays, subject to the law that in every case 

 the refrangibility of the emitted rays is less than that of the 

 incident. This law, which has particular reference to those 

 cases where the incident rays are Newtonic ones, has been found 

 to obtain without exception in all known examples both of fluor- 

 escence and of phosphorescence* ; and, since it comes of itself 



* See Phil. Trans, for 1852, p. 499; and Ann. de Chim. et de Phys. 

 vol.lv. pp. 114 and 117 (1859). In a few instances the incident and 

 emitted rays have been found to be of equal refrangibility. 



