axis, or any other point or pivot of revolution in his presence. 

 Such a result, without rotation or turning round, is plainly im- 

 possible, and the object of all my arguments and experiments is 

 to show that it is so. In this respect they have acted quite in 

 the spirit of the Ptolomeans, who went on continually adding 

 new cycles and epicycles, to explain the phenomena of the uni- 

 verse, till Copernicus displayed to their astonished eyes the sim- 

 ple truth, and demolished the complicated fabric that had been 

 the work of many ingenious minds during many ages. The ro- 

 tation which astronomers ascribe to the moon is just as purely 

 hypothetical and groundless as any Ptolomean epicycle ; yet 

 has this doctrine been allowed to remain for almost two centuries 

 a foul blot on the temple they have reared to the glory of physi- 

 cal science. 



In the article Astronomy, in the Encyclopaedia Edinensis, 

 (I. 510,) said to have been written by " George Buchanan, Esq., 

 Civil Engineer, Edinburgh," the moon's rotation is thus described 

 and demonstrated ; — '' From the motion of the solar spots has 

 been inferred the rotation of the sun on his axis. The same 

 conclusion is drawn in regard to the moon, from the apparent 

 rest of her spots. For, as we go round and round a building 

 when we wish to have a view of it on every side, in the same 

 manner would the moon present to us, in succession, every por- 

 tion of its surface, if, without moving on its axis, it only revolved 

 round the earth, the appearances being evidently the same as if 

 the earth loent round and round the moon at rest. Thus, if a 

 spectator on the earth should observe a remarkable spot, S, (fig. 

 8,) on the centre of the full moon at M, he would evidently lose 

 sight of it by the time the moon, if immovable on heraxis^ arrived 

 at her quarter at m ; and another spot, 5, which he did not at first 

 observe, would now occupy the same centre position ; and in order 

 that the same spot as at first should still be observed on her 

 centre, it would be absolutely necessary for her to make a quar- 

 ter rotation in a direction contrary to that of her revolution. 

 When the moon, therefore, in revolving round the earth, still 

 presents to us a figure whose general appearance, though ex- 

 tremely irregular, is always the same, and which must on this 

 account be undoubtedly the same half of her surface, we may be 

 assured that the moon has really a rotation on its axis, in a di- 

 rection contrary to and keeping exact pace with her revolution 

 round the earth." 



To the eye of common observers the sun and the moon appear 

 to be both alike satellites of the earth, and, as such, to go round 

 about the whole heavens in very nearly the same track. But, 

 if the one of them, the sun, turn on his axis, and, by so turning, 

 show a succession of spots flitting across his disk, should we not 



