Mr. A. Tylor on Tides and Waves. 207 



at its mean distance. The attraction of the moon I calculate to 

 be one fifteenth greater at a point on the near side of the earth 

 than at a point vertically below it on the offside at the antipodes. 

 Every day the change of position of the moon with regard to 

 the earth would affect all weights on the surface of the earth 

 temporarily, but only to the extent of 1 grain in 61 gallons, a 

 quantity which is not susceptible of measurement by a balance. 

 The effect of the moon's direct attraction is really very small 

 on each cubic foot ; but as it affects water at the bottom of 

 the sea nearly as much as on the surface, it amounts to an 

 enormous moving force when a stream 20,000 feet deep is set 

 in motion. It is only perceptible to observation when motion 

 is accumulated by composition at certain points, such as where 

 there is a great composition of forces, as in soundings. Navi- 

 gators do not observe the motion of the tide except near the 

 coast. I calculate the amount in the following manner. If 

 the effective force of the moon has to be multiplied eighty-four 

 times to raise a 12-foot tide at a point of the coast where the 

 sea is 238 feet deep, then the direct effect of the moon's attrac- 

 tion on water 238 feet deep would only be ifoot, or something 

 under 2 inches. Thus I consider 2 inches is the greatest height 

 that the moon could possibly raise the level of the sea under it 

 with 238 feet depth of water, -ff of the elevation of 12 feet 

 being the effect produced in deeper water by the moon and 

 sun, transferred by the composition of forces to shallow water. 

 The drawings (figs. 1, 2, and 3, PI. IV.) from standard works 

 on tides are therefore great exaggerations by their authors; and 

 the descriptions accompany iug them would lead any one to 

 suppose a great heap of water could be rapidly accumulated in 

 the central ocean by vertical attraction on deep water. The 

 authors do not specify how the water is obtained, or whence it is 

 comes, or the data by which they prove such a heaping up 

 possible as is proposed by the equilibrium theory. 



Time is the essence of such an operation, which, if done at 

 all, must be completed in six hours, or a contrary current would 

 set in. The heaping-up movement, to keep up with the rota- 

 tion of the earth, would have, in the latitude of Brest, to make 

 water flow at 11*3 miles per minute, which is clearly impossible. 

 It is not, therefore, surprising that the effect of the tidal wave is 

 hardly perceptible at oceanic islands, whereas, if figs. 1, 2, and 3, 

 PL IV., were correct, it ought to be as large there as on the 

 mainland coast. 



Fig. 1, PI. IV. is an explanation of the tides copied from the 

 ' Penny Cyclopaedia ; ' figs. 2 and 3, PL IV., are from Dr. Lard- 

 ner's 'Astronomy/ pp. 324-5; and my own view is given in 

 fig. 4; so that the reader may compare the different theories. 



