Scientific Intelligence.'-^ Arts. WS 
ated by the combustion of inflammable gas. It is well known 
in mechanics, that a vacuum, in whatever way it is produced, 
forms the source of great mechanical poWer. It was by means 
of a vacuum, produced by the condensation of steam, that Cap- 
tain Savery contrived to raise water in his steam-engine. It was 
also remarked by the celebrated mechanic Dr Hook, in regard 
to some plan which had been proposed for working by means of 
a piston, If,^’ said he, a speedy vacuum could be made un- 
der your piston, your work is done.” It was accordingly, by 
forming this vacuum under the piston by means of the con- 
densation of steam, that Newcomen succeeded in his improved 
stearh-engine; and this continues, indeed, to be still the great prin- 
ciple of the engines of the present day, namely, the creation of a 
vacuum under or above the piston. Mr Brown then proposes 
to create this speedy vacuum by means of the combustion, for 
example, of coal or oil gas, a gas-burner being lighted within 
the cylinder, and allowed to consume the internal air, part of 
which it condenses into water. Now, admitting that this plan 
is practicable, and that the machinery whicli Mr Brown has 
described could be made to work with effect, let us see what 
would be the expence of this power. Coal-gas sells in Edin- 
burgh at 12s., oil-gas at 40s. : take the coal-gas, then, and sup-i 
pose that every cubic foot of this gas is capable of creating an 
equal space of vacuum, — a circumstance which is b}^ no means 
proved even to half the extent; but let this advantage be set 
against the raising of its water of condensation, and other im- 
pediments which the steam-engine may have to encounter ; and 
suppose that a steam-engine consumes 20 feet of steam per mi- 
nute for every horse-power, which will be found near the truth; 
then, by the same rule, a gas-engine would consume the same 
quantity, which is equal to 12,000 feet per day, and would cost 
therefore ^^7, 4s. per horse-power, for gas alone. Such a sum, 
however, would maintain at least 30 horses, and this considera- 
tion alone is sufficient to prove that the engine has no chance of 
success, let its mechanism and operations be ever so perfect; 
unless, indeed, it can be shewn, that every cubic foot of gas is 
capable of creating 30 cubic feet of vacuity, instead of only half 
VOL. XIL KO, 23. JANUARY 1825. X 
