[22] Preface aux Eloges—Œuvres, tom. v. p. 8.
[23] Fontenelle, Pluralité des Mondes, Conversat. 3.
[24] Fontenelle, Pluralité des Mondes, Conversat. 1.
[LECTURE VI.]
THE SAME SUBJECT CONTINUED.
In my last Lecture, Gentlemen, I considered, at some length, the nature of Physical Inquiry in general, and stated to you, in particular, the two lights, in which objects may be physically viewed, as existing simply in space, or as existing in time,—the inquiries, with respect to the one, having regard to the composition of bodies; the inquiries, with respect to the other, having regard to the changes, of which they are either the subjects or occasions, and consequently to their susceptibilities or their powers—their susceptibilities of being affected by other substances, their powers of affecting other substances. I use the word susceptibility, you will perceive, as, in this case, synonymous with what Mr Locke, and some other writers, have denominated passive power, to avoid the apparent verbal contradiction, or at least the ambiguity, which may arise from annexing the term passive to a word, which is generally employed to signify, not the subject of change, but the cause or occasion of change.
Of these two points of view, then, in which an object may be regarded, when the question is put, What is it? we have seen, I hope, sufficiently distinctly, the nature of one. If, in answering the question, we regard the object merely as it exists in space, and say, that it is a compound of certain substances, we mean nothing more, than that, in the portion of space, which we conceive to be occupied by this one imaginary aggregate, there is truly a plurality of bodies, which, though seemingly contiguous, have an existence, as separate and independent of each other, as if they were at the most remote distance; the one aggregate being nothing more than a name for these separate bodies, to which ourselves give all the unity which they have, merely by considering them as one.
The necessity of inquiring into the nature of these separate elementary bodies,—which constitutes one of the two great departments of physical investigation,—we found to arise from the imperfection of our senses, that are not sufficiently acute to discover, of themselves, the component parts of the masses, which nature everywhere presents to us. We are thus obliged to form to ourselves an art of analysis, merely that we may perceive what is constantly before our eyes, in the same manner, as we are obliged to have recourse to the contrivances of the optician, to perceive stars and planets, that are incessantly shedding on us their light.