I have exerted myself to the utmost to ensure the accuracy and completeness of this volume, but I feel conscious that, after all my efforts for this purpose, some errors have crept into it, that many subjects which deserve insertion in it have been omitted, and that many others have been either imperfectly or too briefly noticed. “Yet these failures, however frequent, may,” I trust, “admit of extenuation and apology. To have attempted much is always laudable, even where the enterprise is above the strength that undertakes it. To rest below his aim is incident to every one whose fancy is active, and whose views are comprehensive; nor is any man satisfied with himself because he has done much, but because he conceives little.” When I commenced this work I resolved to leave nothing within its legitimate limits unexamined or unelucidated; and I flattered myself with a prospect of the hours which I should thus “revel away” in a pursuit so congenial to my desires——“the treasures with which I expected every search into those neglected mines to reward my labour——and the triumph with which I should display my acquisitions to mankind.” But these were the dreams of a poet, doomed at last to wake a “Cyclopædist”. The long task which I had undertaken soon exhibited its truly onerous character, and daily grew in urgency, until that which promised to be a pleasure had been transformed into an exhausting and continuous labour. At first, a sacrifice of the hours of leisure only seemed necessary to the undertaking——next, those assigned to professional and business avocations were demanded, and absorbed; but, ere long, one by one, the hours usually devoted to repose were sucked into the insatiable vortex, until the bright beams of the rising sun not unfrequently illumined the lamp-lit study or the gloomy laboratory, and surprised the author, no longer an enthusiast, at his still-enduring task. But long ere this I had learned that to carry out my original resolutions in all their completeness and entirety was impossible, and “that to pursue perfection was, like the first inhabitants of Arcadia, to chase the sun, which, when they had reached the hill where he had seemed to rest, was still at the same distance from them.”[2] All I can further say in reference to this point is simply to assure the reader that three of the elements usually deemed essential to give value to a technological work——viz. zeal, industry, and capital——have not been wanting in the production of the present one;——the first two depending on the author, and the other chiefly on the liberality and enterprise of the publisher. [Footnote 2: Dr Samuel Johnson’s Preface to his English Dictionary.]