96 REPORT—1863. 
incidence of the rays of the flame would in no way subvert the similarity just 
pointed out*. 
Experiment II. 
5. The foregoing experiment recommends itself for the reason of the almost 
total absence of Newtonic and Ritteric rays from the ray-producing source, 
whose presence, at least for the production of the transmutation (8), is not 
wanted. On the other hand, the execution of the experiment would be liable 
to considerable practical, if not other, difficulties ; and hence that next to be 
described may be considered as, upon the whole, perhaps, more hopeful. 
Let, as radiating source, the sun be chosen, and, as test-object, a piece of 
metal—best of all a thin piece of platinum-foil, which place in the focus of a 
large mirror exposed to the sun. If the mirror be of sufficient size, the pla- 
tinum will become incandescent, and may even meltt. Let the former result 
only be supposed to happen. All the three kinds of rays, Ritteric, Newtonic, 
and Herschellic, being present at the focus of the mirror, each will have con- 
tributed a certain share to the production of the temperature of incandescence 
of the piece of platinum exposed to their joint calorific action. Let this 
action, so far as the Ritterie and Newtonic rays jointly are concerned, be re- 
presented by a, and that of the Herschellic rays, by themselves, be denoted 
by @. If the two former species of rays be prevented by absorbents from 
reaching the platinum, but the deficiency of calorific action caused by their 
withdrawal be replaced, either by employing a mirror capable of concentrating 
a pencil of Herschellic rays of the separate calorific action («+/), or by some 
other independent means, then there does not appear any reason why the 
platinum should not be rendered incandescent, or made to emit Newtonic 
rays upon the sole incidence of Herschellic rays, as heretofore upon the inci- 
dence of the unsifted solar beams. An experiment of this nature would bear 
the closest similarity to those by which fluorescent phenomena were first of 
all discovered. - 
Experiment III. 
6. The third and last experiment to be proposed is founded upon the fol- 
lowing considerations :— 
Fluorescence Prof. Stokes is inclined to consider as owing to the vibrations 
of the material molecules of matter when acted upon by incident rays §. 
Adopting this view of the matter, and recollecting that each substance by 
itself constitutes a distinct source of rays, the efficiency of which depends on 
temperature or on impressed molecular motion, it is natural to suppose that, 
in the rays emitted in the act of fluorescence, the spontaneous and incident 
become blended in a certain manner by some kind of interference. That this 
is true to some extent seems to result, among others, from the observed influ- 
ence of temperature on the power of substances to fluoresce ||; consequently, 
the law established by Prof. Stokes with reference to all fluorescent pheno- 
mena may be shown to be capable of a different construction from that usually 
put on it. Remembering that the incident rays, in fluorescence, are either 
* Cf. Part IT. Art. 4, p. 102. 
t Cf. e. g. the accounts of experiments with burning-mirrors in Phil. Trans. 1686, (vol. 
xvi.) p. 852, and 1719, (vol. xxx.) p. 976, some of which refer, if not actually to platinum, 
to silver, which is almost equally refractory. 
¢ For simplicity, the absorption which the Herschellic rays would, practically, undergo 
simultaneously with the remainder has been left out of consideration. 
Phil. Trans. 1852, p. 548. 
I ysl. Stokes) Phil, Trans, 1852, p. 532 and ; (M. O. Fiebig) Pogg. Ann. yol. exiv. 
p. 202 ; 
