第17章

But though the conception of Matter as consisting of dense indivisibleunits is symbolic, and cannot by any effort be thought out, it may yet besupposed to find indirect verification in the truths of chemistry. These,it is argued, necessitate the belief that Matter consists of particles ofspecific weights, and therefore of specific sizes. The law of definite proportionsseems impossible on any other condition than the existence of ultimate atoms;and though the combining weights of the respective elements are termed bychemists their "equivalents," for the purpose of avoiding a questionableassumption, we are unable to think of the combination of such definite weights,without supposing it to take place between definite molecules. Thus it wouldappear that the Newtonian view is at any rate preferable to that of Boscovich.

A disciple of Boscovich, however, may reply that his master's theory is involvedin that of Newton, and cannot indeed be escaped. "What holds togetherthe parts of these ultimate atoms?" he may ask. "A cohesive force,"his opponent must answer. "And what," he may continue, "holdstogether the parts of any fragments into which, by sufficient force, an ultimateatom might be broken?" Again the answer must be -- a cohesive force.

"And what," he may still ask, "if the ultimate atom were reducedto parts as small in proportion to it, as it is in proportion to a tangiblemass of matter -- what must give each part the ability to sustain itself?"Still there is no answer but -- a cohesive force. Carry on the mental processand we can find no limit until we arrive at the symbolic conception of centresof force without any extension.

Matter then, in its ultimate nature, is as absolutely incomprehensibleas Space and Time. Whatever supposition we frame leaves us nothing but achoice between opposite absurdities.*

§17. A body impelled by the hand is perceived to move, and to movein a definite direction; doubt about its motion seems impossible. Yet wenot only may be, but usually are, quite wrong in both these judgments. Here,for instance, is a ship which we will suppose to be anchored at the equatorwith her head to the West. When the captain walks from stem to stern, inwhat direction does he move? East is the obvious answer -- an answer whichfor the moment may pass without criticism. But now the anchor is heaved,and the vessel sails to the West with a velocity equal to that at which the captain walks. In what direction does he now move when he goes fromstem to stern? You cannot say East, for the vessel is carrying him as fasttowards the West as he walks to the East; and you cannot say West for theconverse reason In respect to things outside the vessel he is stationary,though to all on board he seems to be moving. But now are we quite sure ofthis conclusion? -- Is he really stationary? On taking into account the Earth'smotion round its axis, we find that he is travelling at the rate of 1000miles per hour to the East; so that neither the perception of one who looksat him, nor the inference of one who allows for the ship's motion, is anythinglike right. Nor indeed, on further consideration, do we find this revisedconclusion to be much better. For we have not allowed for the Earth's motionin its orbit. This being some 68,000 miles per hour, it follows that, assumingthe time to be midday, he is moving, not at the rate of 1000 miles per hourto the East, but at the rate of 67,000 miles per hour to the East. Nay noteven now have we discovered the true rate and the true direction of his movement.