THE TIDES 159 



his "wild speculation" in the chief publication of the 

 world! 



NEWTON'S THEORY OF THE TIDES 



Inasmuch as the tides rise it was natural enough for 

 Newton to surmise, in the first instance, that they are 

 caused by gravitation lifting the waters away from the 

 earth proper ; and inasmuch, also, as there exists a coin- 

 cidence between the moon's schedule and the schedule of 

 the tides, it was not less natural for him to infer, at least 

 provisionally, that the moon, rather than the sun, is the 

 primary tidal force. Accordingly, he conceived the moon 

 as drawing the oceans immediately under her away from 

 the earth's solid part or kernel, and the kernel in turn 

 away from the nether oceans, thus causing the double 

 tide that observation reveals to exist. 



When he came to compute the relative attractions of 

 the sun and moon, however, he found that, after making 

 due allowance for their respective masses and distances, 

 the attraction of the former upon our earth is 180 times 

 stronger than the lunar attraction. Such a result was, of 

 course, incompatible with his primary hypothesis that the 

 moon is the greater tidal force (a hypothesis which, alas! 

 he took to be axiomatic), so he cast about in his mind for 

 a way to reverse the order of their potency, and to twist 

 things to fit. 



Continuing his argument, he reasoned that the 

 waters that actually compose the tidal hillock are to be 

 differentiated from the level mass of the ocean in this, 

 that they are the part displaced, having to be drawn in 

 from the surrounding regions. Such being the case, the 

 attraction of the moon which drew them in could not have 

 been, at first, vertically exerted upon them, but obliquely, 

 and the same reasoning applied equally to the sun's at- 

 traction. It consequently followed, mathematically, that 

 the tidal forces vary, not as the inverse squares (the law 

 of gravitation) of the distances of the sun and the moon, 

 but as their inverse cubes. Computing anew on this 

 basis Newton made out the moon to be about four times 



