A Letter to the Right Honourable George Earl of Macclesfield: Concerning an Apparent Motion Observed in Some of the Fixed Stars. By James Bradley, ...

printed in the year, 1747 - 43 pages
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Page 40 - And on the other hand, if our own system be at rest, and any of the stars really in motion, this might likewise vary their apparent positions ; and the more so the nearer they are to us, or the swifter their motions are, or the more proper the direction of the motion is, to be rendered perceptible by us.
Page 16 - ... the inclination of the earth's axis to the plane of the ecliptic, and more remotely upon the variations in that inclination known as precession and nutation.
Page 17 - ... gradual diminution of the obliquity of the ecliptic, it does not arise only from an alteration in the position of the earth's axis, but rather from some change in the plane of the ecliptic itself; because the stars, at the end of the period of the moon's nodes, appeared in the same places, with respect to the equator, as they ought to have done, if the earth's axis had retained the same inclination to an invariable plane."2 FRENCH ASTRONOMERS Meanwhile, astronomers across the channel were by...
Page 13 - Moon upon those parts, the plane of the Moon's orbit being at one time above ten degrees more inclined to the plane of the equator than at another, it was reasonable to conclude, that the part of the whole annual precession, which arises from her action, would in different years be varied in its quantity ; whereas the plane of the ecliptic, wherein the Sun appears, keeping always nearly the...
Page 9 - Stars fometimes to dance to and fro, fo much that it is difficult to judge when they are exactly on the Middle of the Wire that is fixed in the common Focus of the Glafles of the Telefcope. I...
Page 42 - ... there taken, as a most valuable criterion, whereby I may judge of the accuracy of those that are made at the Royal Observatory; and, as a lover of science, I cannot but wish that our nation abounded with more frequent examples of persons of like rank and ability with your Lordship, equally desirous of promoting this, as well as every other branch of natural knowledge, that tends to the honour and benefit of our country.
Page 14 - ... yet the apparent annual precession might sometimes exceed, and sometimes fall short, of that mean quantity, according to the various situations of the nodes of the moon's orbit.
Page 16 - I found it necessary to continue my observations through a whole period of the moon's nodes; at the end of which I had the satisfaction to see that the stars returned into the same positions again ; as if there had been no alteration at all in the inclination of the -earth's axis: which fully convinced me that I had guessed rightly as to the cause of the phenomena. This circumstance proves likewise that, if there be a gradual diminution of the obliquity of the ecliptic, it does not arise only from...
Page 39 - ... forementioned points indeed can be settled only on the supposition that the angular distances of these stars do continue always the same, or that they have no real motion in themselves, but are at rest in absolute space. A supposition which, though usually made by astronomers, nevertheless seems to be founded on too uncertain principles to be admitted in all cases.
Page 16 - THAT inclination to diminish regularly; if this phenomenon depended upon such a cause, and amounted to 1 8" in nine years, the obliquity of the ecliptic would, at that rate, alter a whole minute in thirty years; which is much faster than any observations, before made, would allow. I had reason, therefore, to think that some part of this motion at the least, if not the whole, was owing to the moon's action upon the equatorial parts of the earth; which, I conceived, might cause a libratory motion of...

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