DR. CARTWRIGHT.

149

work with ardent spirits, and produce thedesired elasticity of steam with one-half theheat,—hence, in calculating the weight ofthe whole apparatus, the weight of the con-densing water will be trifling, it is thereforethe weigh t of the engine and the fluid inthe boiler which are to be calculated. Forthis object I believe the engine should bedouble, with the steam acting on the top andbottom of the piston, or in two cylinders, theone ascending while the other descends.For the particular case, where such a boat iswanted, I believe it is of more importance tohave a light and compact engine, than to havetoo much regard to the economy of fuel, un-less the additional weight of the fuel to gotwenty miles would be more than the addi-tional weight of the engine to economize theheat. To gain power in a small space, howwould it answer to make the boiler sufli-