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Updated: August 21, 2024
The explanation by Newton of the observed facts of the motion of the moon, the way he accounted for precession and nutation and for the tides; the way in which Laplace explained every detail of the planetary motions these achievements may seem to the professional astronomer equally, if not more, striking and wonderful; but of the facts to be explained in these cases the general public is necessarily more or less ignorant, and so no beauty or thoroughness of treatment appeals to it or excites its imagination.
His argument was, that if it were a mere shell filled with liquid, precession and nutation would be much larger than they are observed to be. For the shell alone would follow the pull of the sun and moon on its equatorial girdle, leaving the liquid behind; and being thus so much the lighter, would move the more readily.
The numerous florets, which constitute the disk of this flower, contain in each five males surrounding one female, the five stamens have their anthers connected at top, whence the name of the class "confederate males;" see note on Chondrilla. The sun-flower follows the course of the sun by nutation, not by twisting its stem.
I remember that Perry was very much excited when I told him about this Dead World, for he seemed to think that it explained the hitherto inexplicable phenomena of nutation and the precession of the equinoxes. When the two upon the lidis had come quite close to us we saw that one was a man and the other a woman.
The way in which he was led to the detection of the nutation is strikingly illustrative of the extreme care with which Bradley conducted his observations. He found that in the course of a twelvemonth, when the star had completed the movement which was due to aberration, it did not return exactly to the same position which it had previously occupied.
Because light travels with enormous rapidity, the shifting is very slight; and each star returns to its original position at the end of a year. Bradley's second great discovery was finally ascertained in 1748. Nutation is a real "nodding" of the terrestrial axis produced by the dragging of the moon at the terrestrial equatorial protuberance.
Moreover, the points to which measurements are referred are themselves in motion, either continually in one direction, or periodically to and fro. The precession of the equinoxes is slowly progressive, or rather retrogressive; the nutation of the pole oscillatory in a period of about eighteen years.
These movements consist of revolving nutation, the bending to and from the light, and in opposition to gravity, those caused by a touch, and spiral contraction. It is rash to differ from so great an authority, but I cannot believe that one at least of these movements curvature from a touch is thus caused.
I remember that Perry was very much excited when I told him about this Dead World, for he seemed to think that it explained the hitherto inexplicable phenomena of nutation and the precession of the equinoxes. When the two upon the lidis had come quite close to us we saw that one was a man and the other a woman.
The movement is, in fact, a continuous self-bowing of the whole shoot, successively directed to all points of the compass; and has been well designated by Sachs as a revolving nutation. As this movement is rather difficult to understand, it will be well to give an illustration.
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