(102.) One of the methods of equalising the varying force of expanding steam, would be to work it at the same time in two cylinders connected with the same beam; so that while its force in one would be augmented, its force in the other would be diminished, the combination of the two producing a uniform effect. Soon after the expansive principle was promulged by Mr. Watt, this expedient was accordingly resorted to by an engineer named Hornblower. [Illustration: _Fig._ 30.] In the year 1781, Hornblower conceived the notion of working an engine with two cylinders of different sizes, by allowing the steam to flow freely from the boiler until it fills the smaller cylinder, and then permitting it to expand into the greater one, employing it thus to press down two pistons in the following manner. Let C, _fig._ 30., be the centre of the great working-beam, carrying two arch heads, on which the chains of the piston rods play. The distances of these arch heads from the centre C must be in the same proportion as the length of the cylinders, in order that the same play of the beam may correspond to [Pg175] the plays of both pistons. Let F be the steam-pipe from the boiler, and G a valve to admit the steam above the lesser piston. H is a tube by which a communication may be opened by the valve I, between the top and bottom of the lesser cylinder B. K is a tube communicating by the valve L, between the bottom of the lesser cylinder B and the top of the greater cylinder A. M is a tube communicating, by the valve N, between the top and bottom of the greater cylinder A; and P a tube leading to the condenser by the exhausting valve O.