THE MOON'S MOTION.
STE—Having waited some weeks to see if any one else, in the great cause of correctly diffusing scientific knowledge, would give a good solution of this question, I venture to offer you the following remarks.
• The discussions on this subject have really illustrated little more than the imperfect use of language by most writers on it, though they show the astronomers, as represented by Herschel!, to be the least skilled and accurate in the use of language ; a result which is not surprising, as the legal gentle- man, who originated the discussion (and very usefully I think), not only has the advantage in accuracy, but was more likely to have had it, if he also understands astronomy. It is to the earth that the description is usually applied, that it turns or rotates on its own axis ; and which phrase describes sufficiently, however incorrectly, one of the motions of the earth.
Different opinions, however, may well be held how far that description is correct ; for that motion of the earth is not strictly a turning on its own axis, that phrase strictly describing only the motion of a globe, or circular wheel ; when turned on a pivot which passes through the centre of such globe or wheel, such pivot, supposed to be fixed in space, a condition, of course, im- possible to anything on this earth ; whilst the motion of the earth, which would otherwise be similar, is altered by the progress of the earth round the sun, and by the variations, or mutations, iu the earth's movements.
& course, also, that motion of the earth and moon which tends to be strictly a rotation round some axis, is altered and varied in space by the facts that, whilst the moon is making its monthly journey round the earth, the moon and earth together are making a yearly journey round the sun. The motions of the earth and moon therefore, most alike, are not only different from one another, but are neither of them strictly a rotation round any axis considered as a fixed point or line in space. All parties being really agreed that the motion of the earth above de- scribed is not the same as any one motion of the moon, it follows that it is vain to attempt, as Herschell does, to describe those two very different mo- tions, or modes of movement, by the same phrase or words, and doing so, can only create confusion. Now the real fact is, that the above motion of the moon, may be described with the nearest practicable approach to accuracy and shortness, by stating " that the moon has a motion which partakes of a rotatory character, and that such motion consists in a turning or rotation on an axis passing through the centre of the earth, (or that the axis on which such quasi rota- tory motion takes place, passes through the centre of the earth), on which axis the moon rotates once during its monthly progress round the earth." Why, therefore, should not that description be used generally, and all
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