lettu5 In t4t EMinr.
TILE moox's AXIAL MOTION.
Sin—Upwards of three years ago, Mr. Jellinger Symons, in a corre- spondence with me regarding some apparatus I had prepared in connexion with this subject, challenged me to a friendly disputation before arbitrating. I accepted this challenge, and Mr. Symons being then in Hereford, was, upon his return to town, to have signified his readiness to bring the matter to issue. I have never heard :mother word from him upon the subject ; which has rather surprised me ; I could only conclude that ho had discovered his position to be untenable. But since he adheres to it still, I think it lies upon him to redeem the gauntlet lie threw down, and that 1 took up.
To prevent 'Misunderstanding, it is best to say that I maintain broadly, and without any qualification whatever, that the moon, in addition to her orbital motions round the earth and the sun, has also a blow but distinct motion upon her axis; which motion would undoubtedly continue, were she to be set wholly free from the attraction of the earth and the sun, (other things remaining unchanged,) and to take her own independent path through space. In other words, that, were the moon's connexion with the solar system to be dissolved, (simply) she would continue to turn her face towards the various portions of the starry heavens in succession, just as olio does now.
I submit the following propositions as amply sufficient to brine the matter to issue, =These, I am prepared to support, either by appeal to undisputed astronomical facts, or by suitable experiments made upon imitative moving bodies.
First, That the moon experiences the alternations of day and night,—sun
rise and sunset„—just as the earth does ; having, however, but twelve and a half days and nights in the year ; thus demonstrating that either the moon turns round on her axis in presence of the sun, or that the sun's huge oases is swung, onto a month, round the comparatively diminutive moon. Secondly, That if we give to a suitable heavy body a motion analogous to that of the moon round the earth, we must needs apply a greater p. e�aeiile force than *could be required to pee the same rate J. mere orbital motion.
Thirdly, That if, whilst such body is in motion, the position of its axis be suddenly changed,—as from the vertical direction to the horizontal,—the axial motion will continue and become manifest ;—its quantity and direction becoming likewise both observable.
Fourthly, That if, whilst such body is in motion, it be suddenly disen- gaged from the moving apparatus, and hung suspended upon a thread, its axial motion will continue, and become manifest ;—its quantity and direc- tion becoming likewise both observable.
Fifthly, That if, to the uppermost pole of such body, we attach the lower end of a tape depending from the ceiling above, such tape will receive a twist, once, for every revolution of such body in its orbit ; thus plainly showing that such body would spin a thread as effectually as a spinning- wheel, though not so rapidly. Sixthly, That if a horizontal tape, or thread, be attached to such body (in a manner convenient for the purpose), such tape or thread will be coiled round such body us it revolves in its orbit, just us a rope is coiled round a capstan. Seventhly, That if a person walk successively, along the four sides of a
square,—as Lincoln's Inn Fields,—le will make, at each of the four corners, one quarter of a turn upon his own axis, all in the same direction ; —their sum being one whole turn. Again, if, by cutting oft' the corners, ho makes his path an octagon, he will make eight fractional turns upon his axis instead of four ; but as each turn will be only one eighth of a whole turn, their sum will be just one whole turn as before. He may next, by a little management at the corners, make his path a sixteen- sided polygon, and therefore make sixteen fractional turns upon his axis, each being one- sixteenth of a whole turn, and their sum one whole turn as before. Now, as a circle may be regarded as a polygon within). infinite number of sides, a person walking round a circle, as Sir John Herschel proposes, maybe equally regarded as making an infinite number of infinitesimal turns on his axis, the sum of which is one whole turn for each circuit completed.
Eighthly, It has been said, that, if it be true that the moon turns upon her axis, such must be equally true of any number of moons ; to wit, of as many as would form a complete ring of moons, somewhat resembling Sa- turn's ring. And if this be true, it must follow that the separate felloes, composing the rim of a wheel, must likewise turn!on their respective axes, whenever such wheel revolves.
I accept this conclusion, which may be put to proof, by mounting a wheel horizontally, upon a circular board, so as to admit of the felloes being dis- connected from, each other. Each felloe must be poised upon a vertical axis, somewhat as a magnetic needle is poised, and means must be provided for temporarily binding the felloes together in such manner as to admit of their instantaneous disengagement whilst the wheel is in rapid motion. A thread, encircling the felloes like a hoop, and to be severed by the flame of a candle, may probably answer this purpose.
If, upon the severance of the constraining thread, the wheel be stopped as speedily as may be, the presence or absence of distinct axial motion in the several felloes, will become manifest ; for, if present, such motion will continue for a short time after the wheel has stopped ; exhibiting the strange spectacle of the felloea all whirling round upon their separate axes, each wholly independent of its neighbour on either side.
Mr. Symons instances the governor balls of a steam-engine, as manifestly disproving the assertion that a body, revolving precisely as they do, has, in addition to its more obvious orbital motion, a second motion round its own axis ; a motion so wholly distinct that it can be either accelerated, retarded, . or stopped altogether, without interfering in the least with the orbital mo- tion of such body. Now, in this instance, chosen by Mr. Symons himself, the facts admit of such positive and 'complete ocular demonstration, that I should not be unwilling to rest the whole case upon it. I am, Sir, your obedient servant, E. HILL.
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