Theories of the Tides. 227 



were produced by the very cause I have assigned. Search the 

 records of philosophy from the earHest periods, and where will 

 you find any thing like this ? Where will you find an instance 

 of a false theory in which no one can point out an error? And 

 yet, while you refuse to admit my theory, you attribute such a 

 miracle to me. You cannot say that my theory does not satis- 

 factorily account for all the phEcnomena connected with the 

 rising of the tides ; and the only objection you can possibly 

 make to it is, that the principle is inadequate ; an objection, 

 begging your pardon, which is founded in your own ignorance 

 of the rate by which the power of gravity diminishes. If you 

 will have it " that the power of gravity deci'eases as the square 

 of the distance increases," then the power of the moon's attrac- 

 tion, at the earth's surface, can only amount to the 144>-thou- 

 sandth* part of the earth's, and a pressure derived from this 

 force can only produce a rise and fall equal to the 14'4-thou- 

 sandth part of the ocean's depth. Supposing the ocean to be 

 twenty miles deep, and allowing it the full breadth of 90°, it 

 will not produce a rise and fall of nine inches ; and we want a 

 principle that will raise the waters four or five fathoms. Choose 

 what principle you will, you cannot make it answer, imless you 

 give up this pretended law, which you know very well has no 

 existence in fact ; and if you cannot tell in what proportion the 

 power of gravit}' decreases with the increase of distance, how 

 can you make it an argument, that the power of the moon's 

 attraction is not quite sufficient to produce the effects my theory 

 requires ? 



In my last pamphlet I proved, in the first place, that the 

 power of gravity does not decrease as the square of the distance 

 increases; for, if it did, the sun's attraction at the earth's sur- 

 face would be fifty times greater than the moon's : and se- 

 condly, that the moon's attraction at the earth's surface might 

 possibly be equal to the 50th part of the earth's, and, in alljoro- 

 babiliiy, is equal to the lOOdth: and, supposing the moon's at- 

 traction in our latitudes to be equal to the 200dth part of the 

 earth's, seven or eightf miles depth of ocean would be quite 

 sufficient to produce the necessary expansion. 



• In the latitude where, according to your and Laplace's theories, the 

 ori^nal tides are produced, it can only amount to the 280-thousandth part 

 of the earth's attraction. 



f It is evident by Mr. Perkins's two experiments, that the degree of the 

 compressibility of water increases in arithmetical proportion with increased 

 d(!pth ; and consequently, twice the depth of ocean will produce a four-fold 

 rise. 8iipposin>r the moon's attraction at the surface of the earth to be equal 

 to tlie 200dth part of the earth's, seven or ci^ht miles depth would produce 

 a rise an<l fall of nearly five fathoms ; and, if it should only equal the 800dth 

 part of the earth's attraction, a depth of fourteen or fifteen miles would raise 

 Y f 2 ^'"^ 



