INTRODUCTION.

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partial view of the bearings of the question, asthe wish of the projector to enlarge or exaggerate.

It has not been so easy a task to insulate theimprovements of each artist, so as to prevent theirmerging into the more imposing labours of namesof greater mechanical reputation, and at the sametime preserve their proper proportion in the historyof the progress of the machine. In noticing these,although brevity was attempted, want of skillmay occasionally have made their description toodiffuse; but of the two extremes, this, perhaps,will be considered to be the more pardonable.

In the plan of this book, it has not been thoughtdesirable to exhibit those machines only whichhave been introduced with effect into prac-tice. This limitation, which would have greatlyabridged the labour of composition, would at thesame lime have led to a most erroneous notion ofthe extent of the ingenuity which has been exertedin bringing steam-engines to their present state ofperfection. Many engines are described whichhave failed upon trial, and these failures have notbeen considered as good reasons for their beingallowed to fall into oblivion, because practice itselfis progressive, and those mechanical difficultieswhich hindered their elfeclive construction may beremoved in advancing towards greater perfection.Other machines will be found detailed, of whichit is doubtful if their authors ever made them thesubjeets of an experimental trial; besides, someprojects, which in the present state of the me-chanic arts, it is probable, would not repay theexpense of an experiment: the schemes whichhave failed, as well as those which are doubtful,have been considered as seeds drifting on a com-mon held, which some random step fixing into