[ 609 ] 
LXIII.— NOTES ON FLUORESCENCE, sy GEORGE FRANCIS 
FITZGERALD, M.a., F.T.c.D. 
[Read May 19th, 1880. | 
THE object of this note is to call attention to the fact that if 
a fluorescent body be heated sufficiently it must cease to be 
fluorescent. 
The method by which I arrived at this conclusion was very 
cumbrous, and when the note was communicated to the Royal 
Dublin Society, Dr. Stoney pointed out that a great simplification 
might be effected by using the method of proof ordinarily employed 
to show that the emissive and absorptive powers of a body are 
equal for each separate ray. In fact, fluorescence consists in a 
body’s absorbing rays of one refrangibility and emitting them at 
another, and consequently for these absorbed rays the emissive 
power of the body cannot be equal to its absorptive power. The 
proof, however, assumes that the bodies are at the same tempera- 
ture, and does not apply to any cases of fluorescence actually 
observed. é 
Let A, be the absorption of an ordinary unfluorescent body, and 
E, its total emission, and R, its reflection of rays that do not 
produce fluorescence in the other body, and let A,, E,, and R, be 
its absorbtion, emission and reflection of rays that do produce 
fluorescence. For the fluorescent body let @,, e,, and 7,, be the cor- 
responding quantities for the non-fluorescent rays, and a,, é,, ey; 
and 7, for the fluorescent rays, e,, represents the rays absorbed as 
fluorescent but emitted as non-fluorescent. 
Now, suppose the two bodies to be spread over two infinite 
parallel planes with perfectly reflecting surfaces, so as to avoid 
the necessity of considering transmitted rays, then for the non- 
fluorescent body we must have— 
Ai) BR, and A.2:Ei= Re 
for the absorbed rays must be the difference between the total 
emission and the reflection, as otherwise the temperature would 
