62 Analyses of Books. [Juny, 
of a process in which the particles of bodies are not carried by 
a too sudden transition trom the fluid to the solid state; but 
gradually approach, and become united by virtue of their mutual 
attractions, as the moieculz of the fluid which had separated them 
go off by evaporation or by other causes. Andin further confir- 
mation of this, it may be urged, that when the crystallization of 
the stalactite carbonate of lime, and of other stalactites, especially 
chalcedony, had been considered as impossible formations, con- 
tradictory to the laws by which Nature acts in the stalactite pro- 
cess, yet the primary form of the carbonate of lime is neverthe- 
less exhibited by the stalactites of the cavern of Antiparos, and 
the primary form of the hydrates of silica by the stalactites of 
blue chalcedony brought from the Hungarian mines.” 
III. On the Application of Hydrogen Gas to produce a moving 
Power in Machinery ; with a Description of an Engine which is 
moved by the Pressure of the Atmosphere upon a Vacuum caused by 
Explosions of Hydrogen Gas and Atmospheric Air. By the Rev. 
W. Cecil, MA. Fellow of Magdalen College, and of the Cam- 
bridge Philosophical Society. 
The author of this paper observes that ‘“ two of the principal 
moving forces employed in the arts are water and steam. Water 
has the singular advantage that it can be made to act at any 
moment of time without preparation ; but can only be used where 
it is naturally abundant. A steam-engine, on the contrary, may 
be constructed at greater or less expense, in almost any place ; 
but the convenience of it is much diminished by the tedious and 
laborious preparation which is necessary to bring it into action. 
A small steam-engine, not exceeding the power of one man, can- 
not be brought into action in less than half an hour; and a four 
horse steam engine cannot be used under two hours’ prepara- 
tion.” 
The engine in which hydrogen gas is employed to produce 
moving forces was intended to unite the two principal advan- 
tages of water and steam so as to be capable of acting in any 
place without the delay and labour of preparation. 
The general principle of this engine, as described by Mr. 
Cecil, is founded upon the property which hydrogen gas mixed 
with atmospheric air possesses, of exploding upen ignition, se 
as to produce a large imperfect vacuum. If two and a halt 
measures of atmospheric air be mixed with one measure of 
hydrogen, and a flame be applied, the mixed gas will expand 
into a space rather greater than three times its original bulk. 
The products of the explosion are a globule of water, formed by 
the union of the hydrogen with the oxygen of the atmospheric 
air, and a quantity of azote, which in its natural state (or den- 
sity 1) constituted °556 of the bulk of the mixed gas ; the same 
-quantity of azote is now expanded into a space somewhat. 
greater than three times the original bulk of the mixed gas ; 
that is, into about six times the space which it before occupied ; 
