imagination; for, as has been shown by the molecular physicists, its dimensions are so inconceivably minute as to far transcend the mechanism of vision, since it would require at least twenty thousand in a line to occupy a medium wave-length of light.
But could the molecule even be magnified to visible and tangible dimensions, with a new light to view it by, it could not by any means be rendered visible, either in whole or in its parts, on account of its incessant and marvelous activity, both interior and translatory. That the gas-molecule did not get its interior motion from the heat of dissociation is certain, for, on being allowed to recombine, it yields up its translatory activity, and with it as many degrees of temperature as disappeared in accomplishing the dissociation. No means of wholly destroying the interior motion are known. By some savants it is regarded as primordial and ultimate. It is highly probable, for reasons which Mr. Taylor has pointed out, that the hydrogen-molecule contains at least four pairs of revolving elements, revolving in different periods, and in contractile orbits, but with periods as undeviating as those of the moons of Mars. It is in the revolving or vibratory constituent of this couple that we seek the final essence of matter, though perhaps not to arrive at it. We must not endow it with gratuitous attributes, but it is surely an entity of some kind, having, in the first place, persistent and regulated motion. Secondly, it has inertia, or mass—the property of conserving vis viva. Thirdly, it has some bond with its fellow by which the motions of both are modified by a constant stress according to a definite law of distance, and this, following Newton, we call attraction. Fourthly, it has the complex property of interchange of momenta, accompanied by that of conserving and compounding motion by angular rebound upon an indefinitely near approach, which we name resilience, or repulsion. Dimension it need not have, nor any other property of masses; but nobody has ever yet succeeded in getting rid of the above four. This is not universally recognized, however, and the recent controversies of philosophy are owing to the strenuous attempts to reduce the number, especially of those called occult. Motion being in our ordinary experience a result, has not been so classified, and indeed has only more recently been recognized as primary. It is with causes that philosophy seeks to deal, and in our experience causation is a chain. Primordial motion, however, is as occult and mysterious as static force.
One class of philosophers, recognizing the self-existent character of motion, has exhausted ingenuity in the effort to deduce attraction from it, of course wittingly or unwittingly bringing into co-operation the occult force inertia, to obtain vis viva. Another class would deduce all motion from attraction: while in the attempt to contrive a mechanism to explain resiliency—the most incomprehensible of all in a body without parts—immensely greater complications and difficulties
- Annual Address before the Philosophical Society of Washington, 1882, p. 24.