86 FROM NEBULA TO NEBULA 



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 

 stronger, tidally, than the sun, instead of 180 times 

 feebler. 



Observation, from Newton's day to this, has failed to 

 reveal any signs of a separate double solar tide, which 

 theory indicates should exist. According to modern com- 

 putations, the ratio of the two tidal forces is, roughly, two 

 to one instead of four to one ; hence the academical argu- 

 ment for the visibility of such a separate solar tide looms 

 stronger to-day than it appeared in Newton 's age. He 

 sought to explain the physical absence of this tide by 

 postulating a merger of the solar with the lunar tide, at 

 one time augmenting and at another offsetting it, ac- 

 cording to the relative angular positions of the two bodies 

 with respect to the earth. 



Now, although it is quite true that there is a startling 

 coincidence between the measure of the daily advance of 

 the moon eastwardly in her orbit and the interval between 



