l28 On the Antllunar Tide. [Feb. 



centre ; and as this giavitation far exceeds the dliFerence of her 

 (the moon's) actions on the different parts of the earth, the effect 

 that will result from these inequalities of the actions of the moon 

 will be only a small diminution of the gravity of those parts of the 

 earth, which it endeavoured, on our former supposition, to separate 

 from its centre ; and a smaller addition to the gravity of those parts 

 which it endeavoured to bring nearer to its centre, that is, those 

 parts of the earth which are nearest to the moon, and those which 

 are fartliest from her, will have their gravity towards the earth 

 somewhat abated ; whereas the lateral parts will have their gravity 

 somewhat increased ; so that if the earth be supposed fluid, the 

 columns from the centre, to the nearest and to the farthest parts, 

 must rise till, by their greater height, they be able to balance the 

 other columns, whose gravity is cither not so much diminished or 

 is increa^ed by the inequalities of the action of the moon; and 

 thus the figure of the fluid earth must be still an oblong spheroid. 



*' We have hitherto supposed the earth to fall towards the moon 

 by its gravity. Let us now consider the earth as projected in any 

 direction, so as to move round the centre of gravity of the earth 

 and moon. Jt is manifest that the gravity of each particle towards 

 the moon will endeavour to bring it as far from the tangent in any 

 small moment of time as if the earth was allowed to fall freely 

 towards the moon, in the same njanner that any projectile at our 

 earth falls from the line of projection, as far as it would fall by its 

 gravity in the perpendicular in the same time. Therefore the parts 

 of the earth nearest to the moon will endeavour to fall farthest 

 from the tani^ent, and those farthest from the moon will endeavour 

 to fall least from the tangent of ■all the parts of the earth, and the 

 figure of the earth therefore will be the same as if it fell freely 

 towards the moon ; that is, the earth will affect a spheroidal form, 

 having its longest diameter directed towards the moon."* 



The theory now explained may be resolved, 1 apprehend, into 

 this short and simple proposition : that the waters nearest the moon 

 are drawn from the earth ; and on the opposite side, the earth is 

 drawn from the waters ; in both of which cases they swell into a tide. 



The first part of the proposition has never been contraverted ; 

 but that the earth is drawn from the waters, in order to form the 

 antllunar tide, is a point by no means so easily conceded. To me 

 it appears to be contrary to known facts, to the general principles 



« 



The theory, a? condrnsed by M. Laplace, isas follows:—" Une mol<?rHle de 

 la mer, piac'e au (lessons dit so'.i-il, en est plus attiit-e que ie centre dc !a terre; 

 elie tend, ainsi, a se n^parer dc sa surface ; mais elle y est retenue par sa pesanteur, 

 que cede tendance dirainue. Ua denii jour apres, celte niolociile ce trouve en 

 opposition avec le soleil, qui Tatliie alors plus faibleinenl que le centre de la 

 terre; la s;irfa:e dn globe terresfre tend done a s'en separer ; niais la pesanteur 

 de la molecule i'v relient ailachi'e ; cette force est done encore diniinu^e, par 

 raurartion sr.hure, et il est facile de s'assurer, que la distance du soleil a la terre, 

 etant fort »r.iii:!'? velativement an rayon du globe terresire, la diminuiion de la 

 pesanteur daus ce.- deux cas, est a trci-pi.u prcs la meme.'" — Systcmo du Mvnde, 

 5. 274. 



