Dr. C. K. Akin on Calcescence. 29 



purpose): — "It seems highly probable," he says*, "that light 

 and heat occur to us each in two predicaments, the vibratory or 

 permanent, and the undulatory or transient state — vibratory 

 light being the minute motions of ignited bodies, or of solar 

 phosphori, and undulatory or radiant light the motion of the 

 sethereal medium excited by these vibrations — vibratory heat 

 being a motion to which all material substances are liable, and 

 which is more or less permanent, and undulatory heat that 

 motion of the same sethereal medium, which has been shown by 

 Mr. King and M. Pictet to be as capable of reflexion as light, 

 and by Dr. Herschel to be capable of separate refraction." The 

 distinction thus clearly drawn between the separate offices of 

 matter and aether, with reference to radiation upon the whole, is 

 particularly applicable to those which regard the phenomena of 

 ray-reproduction — the " undulatory or transient " reproduction, 

 or, in current parlance, diffusion, being attributable to the 

 agency of sether, and the et vibratory or permanent " reproduc- 

 tion, or, as designated above, renovation, to the intervention 

 of matter. 



3. Transmutation. — Of the many phenomena of nature which 

 belong to the domain of renovation, only two (or, rather, one 

 only) have been hitherto investigated — namely, fluorescence and 

 the cognate phenomenon of phosphorescence. Fluorescence may 

 be defined as a case of renovation in which the emitted rays 

 belong to the order of the visible, and the incident, which are 

 the cause of the emitted, either to the same order, or to a higher 

 order, as regards refrangibility, and where emission apparently 

 ceases with incidence ; while phosphorescence has to be consi- 

 dered as a case of fluorescence, distinguished from ordinary 

 fluorescence by a sensible protraction of emission beyond the 

 duration of incidence f. 



The phenomena of fluorescence, if not of phosphorescence, are 

 specially interesting from their having evidenced the change of 

 refrangibility to which rays are liable in the act of renovation — 

 visible rays having been transmuted by the agency of fluores- 

 cent matter into visible rays of different colour, and invisible 

 rays actually transmuted into visible rays. As will presently be 

 shown, however, the range of possible transmutations has been 

 hitherto far from exhausted; and besides the transmutations 

 observed in fluorescence, a number of others seem a priori 

 capable of being effected, some of which it would be highly 

 interesting to realize. For this purpose it is first necessary to 

 consider the constitution of the spectrum of a solar or other 

 similar beam of rays. Any such spectrum, as is well known, 



* Phil. Trans, for 1802, p. 47. 



t See English Cyclopaedia (Arts and Sciences), vol. iv. p. 124. 



