1517. | during the Year 1816. 17 
the other gases to it, in that case gaseous bodies may be reduced 
under three classes. In the first class the specific gravity of the 
gas and the weight of its atom are represented by the same number. 
In the second class the weight of the atom is double the specific 
gravity; and in the third class the weight of the atom is four times 
the specific gravity of the respective gases. 
5. tom of Strontian.—By a set of experiments given in the 
Annals, vii. 399, 1 determined the weight of an atom of strontian 
to be 6°449. Probably the true number is 6°500, which would 
make an atom of strontian 52 times heavier than an atom of 
hydrogen. 
VI. LIGHT. 
1. Phosphorescence of Bodies.—Beccaria’s curious experiments 
on the light emitted by most bodies when suddenly carried into a 
dark place after being exposed to the direct rays of the sun, which 
were published many years ago in the Memoirs of the Bologna 
Academy, are known, I presume, to most of my readers. Since 
that time several additional facts have been brought to light, parti- 
cularly by Mr. Canton, who contrived a substance possessed of this 
quality in an eminent degree. Theodore von Grotthus has lately 
made known a natural substance which possesses this phospho- 
rescent property ina much higher degree than any other hitherto 
observed. He has published a detailed description of the pheno- 
mena exhibited by this new body, and has at the same time con- 
trived an elaborate theory, which he considers as affording an expla- 
nation of phosphorescence in general. (Schweigger’s Journal, 
xiv. 133.) The substance in question is the reddish violet fluor 
spar from Nertschinsk, belonging to that variety of fluor spar long 
known to mineralogists under the name of chlorophane. This sub- 
stance, when slightly heated, gives out a copious emerald-green 
colour. Even the heat of the hand is sufficient to produce the 
effect. If it be exposed to the light of the sun, or of a candle, and 
afterwards taken into a dark place, it emits light, and continues to 
do so for along time. Grotthus compared it thus circumstanced 
with Canton’s pyropborus, and found it to shine much longer, and 
with more brilliancy. His theory of phosphorescence is, that the 
solar light upon the surface of the phosphorescent body between its 
elementary poles is decomposed into its elementary electrical prin- 
ciples, namely, plus and minus electricity, and that the subsequent 
union and escape of these elements of light occasion the phospho- 
rescence of the body. This hypothesis the author illustrates at 
great length, and endeavours to show that it agrees with the expe- 
riments and observations of Dessaignes when properly interpreted. 
{ have not room here to examine in detail the grounds upon which 
this hypothesis is supported ; nor indeed can I say that I fully under- 
stand it. I conceive it will be sufficient to refer those readers who 
wish to go into the subject to the paper itself. It is entitled, Ueber 
einen neuen Lightsauger nebst einigen allgemeinen Betrachtungen 
Vox. IX. N° J, B 
