XIV

PREFACE.

each of whom knows only the application of those prin-ciples to his own art. The farrier, the locksmith, thecutler, know how to work iron; but each of them knowsonly the manner of working which he has learnt, and isperfectly ignorant that the art of working iron has generalprinciples, which would be infinitely useful to him in a* great number of unforeseen cases, to which his commonpractice cannot be applied.—’Tis only by bringing thearts as it were to approach to one another, that we canmake advances towards their perfection : we shall thusput them in a condition of mutually illustrating one ano-ther, and perhaps of producing a great number of usefuldiscoveries : ’tis only by this means that we can knoweffectually their true principles, and enable them to receiveassistance from theory.”

It were to be wished,, that convenience had permittedthese reflections to have had their full influence in the ex-ecution of the work. The history is published in detachedand independent pieces, each containing a minute detail*of the whole series of operations of one art, with descrip-tions and plates of all the instruments made use of; it isdesigned not only to supply the philosopher with the know-ledge otherwise obtainable only among workmen, and toentertain the mind with the history.of - human inventions,but likewise to enable persons to exercise the respective-trades in places where workmen are wanting.

It is obvious that this plan does not at all interfere withmine, and that the views of the two undertakings are essen-tially different. It is not my design to dwell upon de-,scriptions of common and merely manual practices, to give,

particular.