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94 be realized in thought, whatever ground there may be for dissenting from the opinion of Sir W. Hamilton ("Lectures on Metaphysics," Boston edition, p. 385), that "we cannot represent extension to the mind except as colored."

Thus the solid, tangible reality, craved by Prof. Tyndall's "scientific imagination," wholly vanishes from the "seeking intellect" the moment this intellect attempts to grasp it apart from the notion which is said to presuppose it as its necessary substratum. If the deliverances of the scientific imagination are authoritative in science, the notion of the primordial atom must be relegated to the regions beyond the bounds of scientific thought.

There is another and very obtrusive aspect of the atomic theory in which its utter inability to satisfy the demands of the "scientific imagination" has long since been recognized. As I have already shown, the atomic theory, in whatever form it is held, presupposes the separation of the atoms by void, interstitial spaces. The only difference of opinion respecting these spaces is as to their magnitude, the emergencies of the modern theories of heat and light having led to the supposition that even in the case of the purely hypothetical "ether" (which is nothing but a clothes-horse for all the insoluble difficulties presented by the phenomena of sensible material existence—a fagot of occult qualities and principia expressiva whose róle in the material world at large is analogous to the part formerly played by the aura vitalis, and similar phantasms, in the organic world) the interspaces are very great in comparison with the dimensions of the atoms, so that a group of these atoms is not infrequently compared with a stellar or planetary system. Nevertheless, their motions are construed as effects of their mutual attractions and repulsions. But how is the mutual action of atoms existing by themselves in complete insulation and wholly without contact to be realized in thought? We are here in the presence of the old difficulties respecting the possibility of actio in distans which presented themselves to the minds of the physicists in Newton's time, and constituted one of the topics of the famous discussion between Leibnitz and Clarke, in the course of which Clarke made the remarkable admission (Fourth Letter of Clarke, §45, "Leibnitii Opera," ed. Erdmann, p. 762) that, "if one body attracted another without an intervening body, that would be, not a miracle, but a contradiction; for it would be to suppose that a body acts where it is not"—otherwise expressed: inasmuch as action is but a mode of being, the assertion that a body can act where it is not would be tantamount to the assertion that a body can be where it is not. This admission was entirely in consonance with Newton's own opinion; indeed, Clarke's words are but a paraphrase of the celebrated passage in one of Newton's letters to Bentley, cited by John Stuart Mill in his "System of Logic," which runs as follows:

"It is inconceivable that inanimate brute matter should, without