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Show 126 OPPOSING MOTIONS. which actually speed in about twenty-four seconds of time, over a distance equal in !ength to the earth's annual path. Instead, therefore, of being able to question light so as to know whether it be substance or merely motion, we cannot divide time so minutely as to take the slightest note of the duration that It requires to pass from one pole of the earth to the other: and before we can think of the gleam that shoots past us it is millions of miles into the regions of space, shedding its benignant influence upon other and distant worlds. The matter of the earth and also that of the atmosphere, moving so rapidly as th~y do, and in the direction across the path of the sunbeam, must produce an effect different from that which would result if the earth were at rest and the beam only in motion; but as we know nothing of either of the two, we cannot compare them or state what phenomena of nature result from the· compound motion. There is no doubt, however, that the action is greater than it would be if there were only one motion, because we find that to be a general . law of nature. Where two currents of tide meet at sea, the water is trembling and agitated, while a single tide having a greater velocity runs comparatively smooth. When opposing winds strive together upon the face of the waters, the waiers are not only thrown into commotion, but a vortex is formed, a cloudy pillar twines upward, and if the striving winds are powerful, and their strife long continued, a cloud may be made to ascend, which may be borne landward, and fall in deluge and devastation, or falling seaward it may scatter navies, and entomb the most gallant vessels in the deep. So also in smaller matters, opposing the direction of a motion by another motion gives to the colli sion the joint force of both. If stopped at the same length, a blow hits harder when received on the ad .. vancing arm, than when on the arm at rest: the shock of one carriage coming into collision with FINENESS OF LIGHT. 127 another one from the opposite or a cross direction !s mu?h greater than "":he~ the one carriage is stand .. mg shU; ~nd that agam IS greater than if they are both movmg one way, and the swift one runs up on the slow. In all these cases, and in every 1 ~as~ t~at we can examine, the swifter of the two f'Impmgmg substances produces a proportionally greater effect than the other. Soft iron can be made to move so rapidly as not only to cut hardened steel as freely as a steel saw cuts soft timber, but it can be made to burn the steel as easily as if that were the most inflammable of substances. The purest water of the brooks. and str~ams wears away their channels; and the wmds, whiCh are but the thin air in motion, level the abodes of man with the earth and sweep the productions of the earth into the 'Sea~ nor is there the ]east doubt that if a spider's thread of sufficient length, and no thicker than those threads generally are, could be borne onward aO'ainst the globe with sufficient velocity, it would ~leave the globe asunder more easily, and in less time, than the arrow of Tell cleft the apple on the head of his son. If light and heat (for in the beams of the sun they come together, and have many curious combinations m them) be matter, they must be matter in a state o~ far more minute division than we can ever observe With all our artificial helps. Were they of the size of ~he most minute grains of dust even of that WhiCh floats invisibly when the im~ediate rays of the sun_ are not adn:titted into t~e best-lighted room, but which those duect rays disclose as "the light motes that.dance in the beam," they would tell upon the earth hke cannon-shot, and it would have been long_ ere now pounde~ to dust; but instead of that, they are the most kmdly as well as the swiftest m~ssengers that visit our abodes ; and though they brmg us no matter that we can know by bringing it to the test of matter, they bring us active energy, |