58 



expect to see the same effect produced by the rotation of the other 

 moving body, the moon, in circumstances so precisely similar ? 

 No, says Mr B. ; for, though the flitting of the spots across the 

 sun's disk is the effect, the sign, and the evidence of his rotation, 

 and, consequently, were he not to rotate, these spots would stand 

 still ; yet, is the standing still of the spots on the moon's face the 

 effect, the sign, and the evidence of her rotation also ! But, on what 

 principle he could found such an answer is anything but evident; 

 and it is astonishing that the statement of his ownargumentdid not 

 make him doubt the truth of the received doctrine on this sub- 

 ject. To make bad worse be proceeds thus; '* 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 portion of its surface, if, without moving on its 

 axis, it only revolved round the earth, the appearances being 

 evidently the mme^ as if the earth went round and round the 

 moon at rest." Such is a specimen of the reasoning with which 

 astronomers attempt to justify their paradox ; and such reasoning 

 has been deemed sufficient to overrule the irrefragable evidence 

 of non- rotation, supplied by the fact of the moon's presenting the 

 same face continually to the earth. So far, however, are the 

 movements, which Mr B. compares, from being "evidently the 

 same" in their results, that by a very simple proof we shall find 

 them to be totally different. I cannot, indeed, conceive, and 

 should like much to be told, how it is possible for every portion 

 in succession, of the surface of any body whatever, whether re- 

 volving in an orbit, or stationary, to be seen by any observer, 

 but in one of two ways : either by the observer's going round it, 

 or by its turning round on its own axis, or some other point or 

 pivot of revolution, in the observer's presence. This alternative 

 affords the true opposites that Mr B. should have contrasted, and 

 not the observer's going round the body, or the body's going 

 round the observer, without '' moving on its axis." 



" If," proceeds Mr B., "a spectator on the earth should ob- 

 serve 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 hei- axis, 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 quarter rotation in a 

 direction contrary to that of her revolution" So far, however, is 

 all this from being " evident" and *' necessary," that it could only 

 happen in the case, which he tacitly assumes without reason or 

 proof, of the moon's moving in her orbit perfectly free from the 

 action of a centripetal force ; or, in other words, if the centripe- 



