7 The object I have proposed to myself, and wherein its distinction exists, may be thus illustrated. A complex machine is presented to the common view, the moving power of which is hidden. Of those who are studying and examining it, one man fixes his attention on some one application of that power, on certain effects produced by that particular application, and on a certain part of the structure evidently appropriated to the production of these effects, neither the one or other of which he had discovered in a neighbouring machine, which he at the same time asserts to be quite distinct from the former, and to be moved by a power altogether different, though many of the works and operations are, he admits, common to both machines. In this supposed peculiarity he places the essential character of the former machine, and defines it by the presence of that which is, or which he supposes to be, absent in the latter. Supposing that a stranger to both were about to visit the two machines, this peculiarity would be so far useful as that it might enable him to distinguish the one from the other, and thus to look in the proper place for whatever else he had heard remarkable concerning either; not that he or his informant would understand the machine any better or otherwise, than the common character of a whole class in the nomenclature of botany would enable a person to understand all, or any one of the plants contained in that class. But if, on the other hand, the machine in question were such as no man was a stranger to, if even the supposed peculiarity, either by its effects, or by the construction of that portion of the works which produced them, were equally well known to all men, in this case we can conceive no use at all of such a definition; for at the best it could only be admitted as a definition for the purposes of nomenclature, which never adds to knowledge, although it may often facilitate its communication. But in this instance it would be nomenclature misplaced, and without an object. Such appears to me to be the case with all those definitions which place the essence of Life in nutrition, contractility, &c. As the second instance, I will take the inventor and maker of the machine himself, who knows its moving power, or perhaps himself constitutes it, who is, as it were, the soul of the work, and in whose mind all its parts, with all their bearings and relations, had pre-existed long before the machine itself had been put together. In him therefore there would reside, what it would be presumption to attempt to acquire, or to pretend to communicate, the most perfect insight not only of the machine itself, and of all its various operations, but of its ultimate principle and its essential causes.