36

Historical Account

cation is of a very recent date. Steam navigation,however, from its great national importance, willdeservedly find a place in a separate division ofthis work.

Of Mr. Hornblower’s engine, but little need besaid, as in practice he was scarcely able to obtaina greater effect from the expansive action of thesteam in two cylinders, than Mr. Watt’s did inone ; and having attempted in vain to procure anextension of the original term of his patent, hewas afterwards prosecuted by Messrs. Boultonand Watt for an infringement on theirs, in usingthe condenser and air-pump.

The principle of the high-pressure steam en-gine depends on the power of steam to expanditself very considerably beyond its original bulk,by the addition of a given portion of caloric, thusacquiring a considerable elastic force, which, inthis case, is employed to give motion to a piston.One of the greatest advantages attendant on em-ploying the repellent force of steam, as in thisform of the engine, consists in an evident savingof the water usually employed in condensation;and this, in locomotive engines, for propellingcarriages, is an object of considerable importance.

Leupold has furnished a description of a high-pressure engine, in a very valuable work on ma-chines, published in 1724 . He ascribes the in-vention to Papin, to whom we have already al-luded as the inventor of the atmospheric engine.The apparatus described by Leupold, consists of