INTRODUCTION. they produced a great revolution in its use and value. Equally simple improvements have produced still more wonderful effects in machines of more elaborate construction-and above all other mechanisms which can be named, on the steamengine. In detailing these, the fastidious feeling which looks only upon the more perfect form of any production has found no place; simple matters, it is hoped, have not been estimated as being unimportant because they are simple, if at the time of their introduction they either produced or gave rise to an improvement in the mechanism. In other cases, where the claims urged by the inventors themselves have somewhat overstepped the limits of a fair valuation, their high pretensions have been softened with a strong leaning towards the most ample estimate; for a bystander's difference of opinion may as often arise from his from the edge, that the workman put it into the upper piecethis can only be done by that sleight of hand which long prac tice gives, and when this sleight is once acquired the workman can do it with ease, without paying any particular attention, so long as he uses the same tool-but a shoemaker is always sorry when he breaks his awl, because he knows very well that he shall be obliged to serve an apprenticeship of several days before he can acquire the necessary sleight of hand with the new tool-if the new awl is more bent than the old one it will come out nearer the edge than it entered; because its point will describe an arc of a less circle-on the other hand if the new awl is less bent than the old awl, the point will come out at a greater distance from the edge, and the work will have a still worse appearance; hence the workman is obliged to make a series of trials until he can attain the necessary sleight of hand for this purpose. It would be very advantageous if all awls had exactly the same degree of bend-but, unhappily, every maker gives his awl a peculiar bend, to the great trouble of shoemakers and other artists who work in leather."-Mechanics' Journal, p. 363, INTRODUCTION. xli partial view of the bearings of the question, as the wish of the projector to enlarge or exaggerate. It has not been so easy a task to insulate the improvements of each artist, so as to prevent their merging into the more imposing labours of names of greater mechanical reputation, and at the same time preserve their proper proportion in the history of the progress of the machine. In noticing these, although brevity was attempted, want of skill may occasionally have made their description too diffuse; 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 thought desirable to exhibit those machines only which have been introduced with effect into practice. This limitation, which would have greatly abridged the labour of composition, would at the same time have led to a most erroneous notion of the extent of the ingenuity which has been exerted in bringing steam-engines to their present state of perfection. Many engines are described which have failed upon trial, and these failures have not been considered as good reasons for their being allowed to fall into oblivion, because practice itself is progressive, and those mechanical difficulties which hindered their effective construction may be removed in advancing towards greater perfection. Other machines will be found detailed, of which it is doubtful if their authors ever made them the subjeets of an experimental trial; besides, some projects, which in the present state of the mechanic arts, it is probable, would not repay the expense of an experiment: the schemes which have failed, as well as those which are doubtful, have been considered as seeds drifting on a common field, which some random step fixing into xlii INTRODUCTION. the soil, they may be quickened into life, and springing forth, become estimable for their beauty or usefulness. It has been easier to find satisfactory reasons for the plan followed in this little work, than for some other circumstances more immediately connected with the compiler. It may have been vanity which, at the commencement of his speculation, flattered him, that what no one had before attempted would be received, if not with favour, at least with indulgence, by those who like himself were busied in the fabrication of steamengines or in directing their application; besides, from accidental circumstances, the compiler was able to bring together, from his own knowledge, many incidents which others, not so favourably situated as he was, were, perhaps, unacquainted with, and would be gratified by knowing. Any apology for imperfect execution, the compiler is aware, can meet but with few claims to consideration for, although in a literary view, it was foreign to the routine of his usual employment, the task was one he imposed on himself. During its whole progress, however, he has been suffering from ill health, and the avocations of his profession having the first claim on that time he was able to devote to anything-will, at any rate, account for the protracted appearance of the concluding portion of his volumes. From the same causes, absence from the sources to which alone he could refer for his authorities, will, it is hoped, be some extenuation for his errors of omission; although, from their number, he fears he cannot altogether hope for pardon. It was wished to have supplied these in an Appendix; but the bookseller fearing that a longer delay in the pub INTRODUCTION. xlii lication of the book would be detrimental to his interest, this apprehension has induced the compiler to trust to a favourable reception, putting it in his power to add what has been overlooked, or forgotten, in a future impression. |