IS 14.] On the Antilunar Tide. 25/ 



Article IV. 



On the Antilunar Tide. By John Campbell, Esq. of Carbrook. 



(To Dr. Thomson.) 

 DEAR SIR, 



I observe in your Number for June last a notice relative to the 

 antilunar tide ; and although your Correspondent has not entered 

 into the subject in such a manner as to require an answer from 

 either the advocates for the Newtonian theory, or from me ; yet, 

 as it affords an opportunity of illustrating a point in which I 

 humbly conceive the opinions I have published in your work have 

 a considerable advantage over those taught in the Newtonian 

 School, I shall offer a few remarks on the article. 



Your Correspondent W., though he does not seem to perceive 

 it, has given you a crude edition of Ferguson's theory. The prin- 

 ciples on which he accounts for the antilunar tide are, — 1. That 

 the farther parts of a fluid body (by which he means the parts near 

 the surface) have greater centrifugal than centripetal force, and 

 would fly off, were they not restrained by the general mass; whilst 

 the near parts (i. e. nearer the centre) have more centripetal than 

 centrifugal force, and would fall to the centre, were they not re- 

 strained by the same cause. 2. That for these reasons a fluid body 

 turning round a centre out of itself must assume the form of an 

 oblong spheroid, gravity and projectile force being the sufficient 

 and obvious cause of each ; that is, he ascribes the antilunar tide to 

 an excess of centrifugal force. According to Mr. Feiguson, the 

 antilunar tide is caused by the centrifugal force of the side of the 

 earth farthest from the moon being increased by the enlargement of 

 the circle round the centre of the orbit in which the earth is sup- 

 posed by him to move. One can understand Mr. Ferguson's prin- 

 ciple. An enlarged orbit travelled in equal time must increase 

 velocity and centrifugal force. The only unfortunate eireumstar.ee 

 in his explanation is, that it is inconsistent with the fact, i he side 

 of the earth farthest from the moon does not always perform the 

 largest orbit, and therefore his ingenious theory cannot be true. 



Tliis insuperable objection evidently occurs with equal force to the 

 opinion of W., who, like Mr. Ferguson, introduces, as the causi 

 the antilunar tide, the excess of centrifugal force in the farthest part 

 of the earth, moving round a centre of itself. For unless the 

 nt of the antilunar side of the earth be eocurvated, round 

 ■ centre out of itself, the circumstances, which in his- opinion ob- 

 ly cause the tide, do not exi--t. Hut, as has been stated in oppo- 

 sition to Mr. Ferguson, the antilunar side of the earth does not 

 always move in a curve concave to the moon; ami therefore the 

 centrifugal force, as introduced by VV., will not apply. As little 

 v. ill the centripetal force avail him; for even were there any foun- 



Vol.IV. N°1V. U 



