44 
Sidereal Astronomy . 
[January, 
of heat upon chemical decomposition has been studied by 
Mohr. In order that a chemical compound may be dissoci- 
ated by heat alone, it is necessary that one or more of its 
constituent elements shall be gaseous at attainable temper- 
atures. When the gaseous element or elements became 
combined, so as to produce a non-gaseous compound, a 
quantity of heat was evolved, — that is, molecular motion 
was arrested : the process of dissociation will therefore be 
accomplished if the quantity of heat lost on combination be 
restored, because the molecular motion of the constituents 
of the compound will then be so great that they will no 
longer hold together. If a large quantity of heat be evolved 
in the formation of any compound we find that it is hard, or 
in some instances impossible, to decompose that compound 
by heat alone. In the formation of carbon disulphide from 
carbon and sulphur heat is absorbed, because the elements 
are transformed from solids into liquids : now carbon di- 
sulphide may be decomposed by the heat of an ignited pla- 
tinum spiral, but in this experiment heat is evolved, the 
amount being equal to that formerly absorbed in the lique- 
faction of the carbon and of the sulphur. 
Looking at the recent researches in chemistry as a whole 
they all point to the advance of the time when chemistry 
shall have become a mathematical science, whose laws 
shall be formulated with the greatest exactness, and whose 
results shall allow of the application to them of mathe- 
matical reasoning. 
IV. SIDEREAL ASTRONOMY: DOUBLE STARS— 
FAR-OFF WORLDS. 
By Camille Flammarion. 
I. General Considerations . 
* N the depths of the heavens, amongst the varied stars 
which shed their silent light above the regions of the 
starlit night, the eye of the telescopic investigator dis- 
covers stars of a particular character, which differ from the 
ordinary stars in their appearance, as also in the part they 
play in the universe. Instead of being simple, like the 
greater majority of the stars of heaven, they are double, 
triple, quadruple, multiple. Instead of being white, they 
