1814.] On the Aniihmar Tide. 12/ 



To prevent misconception it will be proper in the outset to give 

 a distinct view of this part of the Newtonian system ; and for this 

 l)urpose I cannot do better than adopt the words of one of tlie most 

 profound, as well as perspicuous, of Newton's disciples : I mean 

 Mr. M'Laurin, whose Treatise on the Tides has been held to con- 

 tain such a complete exposition of tlie principles on which their 

 existence depend, that succeeding philosophers have directed their 

 labours rather to prove the agreement of the irregularities of the 

 tides with these principles than to investigate the truth of the prin- 

 ciples themselves. 



After describing the spherical figure which the earth, if entirely 

 fluid and quiescent, would assume ; and showing that the introduc- 

 tion of any other force, acting equally on all tlie particles, and in 

 parallel lines, would not alter tliis figure, he thus proceeds : — 

 " But the actions of the moon on dift'erent parts of the earth are 

 unequal, those parts by the general law being most attracted which 

 are nearest the moon, and those being least attracted which are 

 farthest from the moon, while the parts that are at a middle distance 

 are attracted liy a mean degree of force. Nor are all the parts acted 

 on by parallel lines, but in lines directed towards the centre of the 

 moon ; and on these accounts the spherical figure of the earth must 

 aufter some change from the moon's action. 



" Suppose the earth to fall towards the moon, and let us abstract 

 from the mutual gravitation of its parts towards each other, as also 

 from their cohesion, and it will easily appear that the parts nearest 

 the moon would fall with the swiftest motion, being most attracted, 

 and that they would leave the centre or greater bulk of the earth 

 behind them in their fall ; wliile the more remote parts would fall 

 with tlie slowest motion, being less attracted than the rest, and be 

 left a little behind the bulk of the earth, so as to be found at a 

 greater distance from the centre of the earth than at the beginning 

 of tjie motion ; from which it is manifest that the earth would soon 

 lose its spherical figure, and form itself into an oblong spheroid, 

 whose longest diameter would point at the centre of the moon. 



*' Let us now allow the parts of the earth to gravitate tov.ards its 



ilanding their evident coincidence, to dilVorcut and unconnected canscE ; causes 

 which, iiiif'orluiiately for his Ihoory, liavo no existence in nature. M. Lapl.-icf, 

 while, without remark, he adopts the principle, admits that In several respects 

 the Newtonian theory i% erroneous; and ilicrc issonie reason to hold, as will after- 

 wards appear, in ronsidiriii^ their opinir)ns on the causes nhl'-li jirodiice elliptic 

 orhits, lliat both l.aplace and M'l.auriii, the evpositor of Newtdn, iuglit to be 

 ranged in opposition to (lie prii}ci])Ies th<'y have inadvertently admitted. It may 

 not be >t itiiout some Meighl, also, to niention, that the late able I'lofrssor of 

 Natural I'hiloisophy in the Edinburgh University, Mr. Joiiii Koliison, uheii 

 pressed upon the olijection to the cause assigned by Nevvlon for the swelling of 

 the antilunar tide, acknonledi;i-d that the theory was applicable only to the ease 

 iif a fluid ^lulie, and not to the shallow waters on the surt'aec uf the eardi. I am 

 tuli-fiL'd that (he cause absi;:ned is ctpially erroneous, whether applied to a tluid 

 globe or Hlialliiw waters; but it is builicient to slate (he above aeliniinle(li;n)eiit, 

 Coi.taiiii'd in a letter to myself, to show tli;it Professor Robison was salislied that 

 the New toniaii theory na> iuapplitabk to the antiluuar tide. 



