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LECTURE XLIV.

ON TI1E APPEARANCES OF THE CELESTIAL BODIES.

w E are next to proceed to examine the sensible effects produced by thosemotions which we have first considered in their simplest state, and after-wards with regard to their causes and their laws. Many authors havechosen rather to pursue a contrary method, and have attempted to imitate theoriginal and gradual developement of the primitive motions from their apparenteffects. Hut no conception is sufficiently clear, and no memory sufficientlystrong, to comprehend and retain all these diversified appearances with accuracyand facility, unless assisted by some previous idea of the real changes whichproduce them, or by some temporary hypothesis respecting them, which mayhave been of use in its day for the better connexion of the phenomena,although it does not at present deserve to be employed for a similar purpose,in preference to simpler and better theories, which happen to be historicallyof a later date.

The proper motions of the fixed stars, as they are subjected to our obser-vation, undergo two modifications; the one from the relative direction ofthe motion, by which it may be more or less concealed from our view; theother from the proper motion of the sun, and the planets attending him.This motion has indeed only been inferred from the apparent motions of agreat number of stars, which are either partly or totally referable to it, andwhich could scarcely have agreed so correctly as they do, if they had arisenfrom the real and separate motion of each star.

Among the motions of the primary planets, that of the earth itself requiresa principal share of our attention. The apparent places of the fixed stars arenot sensibly affected by the earth's annual revolution: if any of them had beenconsiderably less remote than they are, it is probable that this motion would