which the exhausted hot air passes to the chimney, and past which the air forced into the furnace flows so as to absorb the surplus heat, and D" is a governor. F and G are the inlet and outlet valves of the pump,

and E' the valve for admitting the hot products of combustion to act upon the piston. J, N are communicating pipes between the engine and tubular air-heater or regenerator. The engine exhibited in Paris had two cylinders of 24 inches diameter and

18 inches stroke. The pistons were connected by an overhead beam, and the trunks were 15 inches diameter. The working pressure was 14 lbs. per square inch. The furnace was formed of boiler plate, lined with two rows of fire bricks, between which

the entering air circulated before coming into contact with the fuel, so as to keep the casing cool.

In Wenham's hot-air engine, worked by the products of combustion, a vertical hopper like a retort, and closed by a door, conveys fuel to a grate, whence the products of combustion proceed to the cylinder, which has a large compressor or plunger like Stirling's; and a valve above the piston remains open

for some time in the return stroke to enable the excess of air to escape.

The wasteful character of the steam engine, as a source of motive power, has now become so widely known that public attention has been directed with more ardour than heretofore to the discovery of ex

pedients for its supersession. Of these alternative expedients the most promising seems to be some form of air or gas engine. But all the air and gas engines heretofore devised labour under this radical defect, that only low pressures can be employed in them, and hence only a portion of the energy of the heat can be transformed into power. So soon as

this fault shall have been corrected without the introduction of other sources of loss, the steam engine will be superseded; and there are good grounds for concluding that this result is not far distant, but will soon be achieved.