626 
The Phenomena of Fluorescence. 
October 
The bodily eye looks at the material, and then the mental 
one looks at the immaterial or invisible, and sees how inse- 
parably connected is matter with force. 
P These observations may well apply to the remarkab y 
interesting phenomena of Fluorescence, or m erna ^ 
persion,” for such are the terms given to the modifying effedt 
produced by certain chemical substances upon a particular 
kind of light-energy which may be made to fall upon then J‘ 
The phenomena appear to have been first observed in io 33> 
by Sir D. Brewster, in an alcoholic solution of the green 
colouring-matter of leaves. _ , . , r 
About ten years later Sir John Herschel made further 
observations, and subsequently published a paper on the 
subieCt in the “ Philosophical Transactions for 1045. 
Since then Prof. Stokes, of Cambridge, and other observers 
in England and on the Continent have been making iurther 
researches in Fluorescence. . 
Without detailing the history of the investigations con- 
nected with the subjeCt, we give our readers some ot the 
more interesting and remarkable faCts which have been 
gleaned of late years, as well as some account ol the earner 
discoveries. , . f 
If we put some common paraffin oil, or a solution ot 
sulphate of quinine, into a glass tube or other suitable 
vessel, and then look through it, the liquid will appear quite 
colourless ; but if we allow the light to fall upon it, and 
then view it at a little distance and at a certain angle, some 
parts of the liquid will present a delicate sky-blue tlnge ‘ 
The effedt in the case of quinine is heightened it the souice 
of light is burning magnesium wire. . 
The large number of substances belonging to this class 
are termed fluorescent bodies, because they exhibit pheno- 
mena similar to the examples above given. The term itself, 
however, was suggested to Prof. Stokes by a particular kind 
of fluor-spar which shows this property. 
Again, if we cause a room to be darkened, and allow only 
blue light (i.e., by covering a hole in a window-shutter with 
cobalt-blue glass) to fall upon a glass vessel filled with water 
which has been standing some minutes, on floating a strip 
of horse-chestnut bark upon its surface, in a few moments 
a stream of bluish grey fluid (sesculm) will be seen slow y 
descending from the bark, hanging, in fadt, like a bunch of 
barnacles from an old ocean waif. Or if, under the same 
arrangement of light, or by using even more powerful ab- 
sorbents of the ordinary rays (such as a solution of ammomo- 
sulphate of copper or one of chromate of potash), we look at a 
