21.2 Mr. A. Tylor on Tides and leaves. 



the ellipsoid a l b v M. Arago very justly wrote that M details are 

 the touchstones of theories f and all details are absent in the 

 well-known articles on this subject. In fig. 1 the earth is 

 represented as a circle, and the ocean as an ellipsoid. In figs. 

 2 and 3 the water is the circle, and the earth the ellipsoid. 



According to figs. 1, 2, and 3, PI. IT., the velocity of the 

 tide would be equal at high, low, and half tide to any observer 

 on the earth. 



The greatest action, on the contrary, is shown to be at the half 

 tide, both ebb and flowing, in my diagram, fig. 4, PI. IV. Cap- 

 tain Beechey* remarked that the velocity of the current was 

 greatest at half tide ; and this disproves any theory in which 

 the tide is supposed theoretically equally strong at all parts. 



Dr. Laidnert explained his diagrams, figs. 2 and 3, PI. IV., 

 by stating that the moon forces down the water at the sides at 

 right angles to her direction, and raises it at the two ends of its 

 diameter pointing to her. In figs. 2 and 3, PI. IV., the moon 

 pulls the water in ODe hemisphere and pushes it away in the 

 other. This is the first time that the property of repulsion or 

 forcing has been attributed in this manner to the heavenly bodies. 

 He shows an exactly opposite direction of forces on the near and 

 far side of the earth produced at the same moment by the moon. 



Notwithstanding any language that may be used to make 

 figs. 1, 2, and 3, PI. IV., appear to satisfy the actual tidal con- 

 ditions, it will, I think, be evident to the reader that the posi- 

 tions of the forces as drawn are not in accordance with the ordi- 

 nary laws of mechanics. Herschel refers the reader to his 

 drawing (Astronomy, p. 464 , in which the retardation and acce- 

 leration oi the moon m its elliptic orbit round the earth at a 

 mean distance sixty times the radius of the earth is proved to be 

 according to the law of equal spaces being described by the moon 

 in equal times, and consequent variation of motion. 



The reader is recommended by Herschel to prove the accele- 

 ration or retardation of the tides from the diagram (p. 464 , 

 which is really impossible, as the figure relates to an entirely 

 different case, and is in a part of his book relating to the motions 

 of the mocn. It is admitted that the moon is a free body attracted 

 at a great distance by the earth, and made to mo^ e at varying velo- 

 cities round the earth in a lunar month at a rate dependent, among 

 other causes, upon the relative weights and distances of the moon 

 and earth, and the original impetus and angle at which these 

 bodies were projected into space. The tidal water, on the con- 

 trary, is held as an inseparable mass oi fluid reposing in a basin 

 of earth ; and it travels at the same uniform speed of rotation as 



* Phil. Trans. 1851, p. 711. 



t Larimer's ' Astronomy/ p. 536. 



