( m ) 
Art. 'KX.y .’^Histor^ of Mechanical Inventions and Processes . 
in the Arts. 
*1. The Rev. Mr ^Cecil’s Machine^ in which Hydrogen Gas 
is the Moving Power. ' 
In the second part of the first volume of the Transactions of 
the Cambridge Philosophical Society there is a paper On the 
Application of Hydrogen Gas to produce a Moving Power,” 
with a description of a machine in which it may be employed. 
The general principle seems to be, that a mixture of one por- 
tion of hydrogen gas, with two and a half portions of common 
air, on being exploded, will expand to three times its bulk, and 
then instantly collapse to one-sixth of its original volume. If, 
therefore, a cylindric vessel be provided, separated at one-third 
of its length into two portions, by a valve moving round an 
axis in the line of its diameter (commonly called a throttle- 
valve) ; if there be a solid piston in the shorter portion, and if, 
at the extremity of the longer portion, there be a light valve 
opening easily outward, then, supposing the throttle-valve shut, 
and the piston close down to it, if the piston be drawn up, and 
the mixture of air and hydrogen be allowed to flow in to supply 
the space left by it, until it reach the end of its stroke, if at this 
time the valve be opened, and at the same time a jet of flame be 
made to communicate with the gaseous mixture (by a touch- 
hole in the side of the cylinder), then, an explosion will take 
place, which will drive out the common air from the larger por- 
'tion of the cylinder by the end valve, w^hich will clap to on tlie 
condensation taking place, and the pressure of the atmosphere 
into the rare medium now- in the cylinder, will force down the 
piston until it reaches nearly to the middle valve, when the gas 
is again admitted, the middle valve closed, and the end one 
opened : the ascent of the piston must be operated by the iner- 
tia of a fly-wheel, put into motion by the downward stroke. 
This is somewhat like the process which goes on in a Newcomen’s 
engine. The atmosphere is the moving power in both, and the 
steam and cold water jet in the one, perform the same offices as 
the hydrogen and jet of flame in the other. 
