ON THE TRANSMUTATION OF SPECTRAL RAYS, 97 
Ritteric or Newtonic ; whilst the spontaneous rays of substances, at the tem- 
peratures at which their fluorescent nature has been investigated, are of the 
Herschellic species; the transmuted or resultant rays, finally, being of the 
Newtonic species; the law adverted to, which requires the transmuted rays 
to be of inferior refrangibility to the incident, may be interpreted also as im- 
plying that the transmuted ray should be of a mean between the incident 
and spontaneous in regard to refrangibility*. Assuming such to be the case, 
the question becomes natural whether, if the order of the rays employed in 
ordinary fluorescence were reversed, by taking for test-object a substance 
naturally emitting Ritteric rays (either alone or in sensible proportion with 
others), and allowing Herschellic rays to be incident on it, the result might 
not be the same as in fluorescence—namely, an emission of Newtonic rays, 
seeing that the circumstances of the experiment, though reversed, are essen- 
tially the same in the two cases. 
7. As objects of experiment, many different kinds of flame might be em- 
ployed, as, likewise, the electric vacuum-discharge. Upon the whole, however, 
of the three experiments proposed, least reliance should perhaps be placed on 
the present, as having the least basis of fact, but principally conjecture, to rest 
upon. The views upon which it is founded imply also a contradiction of the 
principles by which the preceding two experiments are supported, and, if 
pushed to extremes, would similarly be in opposition to certain facts of fluo- 
rescence; nevertheless they will probably be found to accord with truth 
within limits. 
8. The question which has been advanced for solution in this paper, and 
the experiments proposed, might naturally lead to the- consideration of some 
incidental subjects, the most important of which may be worthy of mention. 
The first experiment suggests an investigation of the mode of action of foreign 
matter, whether in the solid or gaseous states, upon comburescent gases or 
flames with reference to the rays emitted by the same ; the second experiment 
involves some discussion of the incandescence of matter in its relations to 
various other similar phenomena ; whilst the third might throw some light on 
the action of gaseous incandescent matter upon rays in general. The bearing 
of all the three experiments, and the considerations which they imply, on the 
subject of ray-absorption are too evident to need pointing out. 
Appendix. 
9. In this Appendix it is intended to present a short historical review of 
the several publications on the collateral phenomena of fluorescence, alluded 
to in the beginning of this paper, which have come to the knowledge of the 
author. They almost all owe their origin to the following observation by 
Fusinieri, which, however, is generally, though erroneously, ascribed to Mel- 
loni. Fusinieri had noticed, and published his observation as early as the 
* The account of the origin of fluorescence given by Prof. Stokes (see Phil. Trans. 1852, 
p. 584) seems to leave it doubtful whether fluorescence depends on the cooperation of the 
spontaneous rays with the incident, or not; for, though some kind of interference is men- 
tioned, the expression seems to refer to the successive impulses given to a molecule by a con- 
tinually impinging ray, rather than to the mutual action of the incident and spontaneous rays. 
On the other hand, though independently formed, the speculations put forth in the text bear 
some similarity to the theory of fluorescence suggested by M. Lommel, in Pogg. Ann. 
vol. cxvii. p. 642 (Dec. 1862). This writer, however, mistakes in stating that the wave- 
length of the transmuted beam is necessarily equal to the difference of the waye-lengths of 
_the incident and spontaneous rays, which is not in accordance with facts, 
HE 
