214 Mr. A. Tylor on Tides and Waves. 



tion V n E, which is that of the line of rotation. In an inland sea 

 like the Mediterranean, where the deep water is 6000 feet, the 

 movement of the tide on the coast is often not more than 1 foot, 

 There are 7-feet tides in one or two places in the Mediterranean 

 where the contour of the coast is like our Bristol Channel. 



If the deep water in the Mediterranean Sea were one twelfth 

 of the depth of that in the Atlantic, we should expect a 1-foot tide 

 there in place of a 12-feet, according to the law of composition 

 of forces*. The peculiar circumstances of the Mediterranean 

 make the tides much smaller than I should have calculated from 

 the experience of the Atlantic. Taking 6000 feet as the basis of 

 the deep water and 9 inches as the tide, diffusion of the tidal force 

 from deep central to surrounding shallow coast-basins seems to 

 absorb § of the force. The proportion of deep water is very small. 



The Mediterranean standard of rates of depths of ocean to 

 height of tide along its coasts, seems to match more with 

 Pacific and west-coast-of-America standards than with the obser- 

 vations on the eastern Atlantic coast. The European tides seem 

 exaggerated, even when compared with the east coast of America. 

 This may be explained by less diffusion of tidal force and the 

 contour of the sea-bottom on our coast being more favourable 

 to receiving impulses giving velocity to the coast-water than 

 that on the east coast of America. For want of space I have 

 hardly been able to allude to the solar influence of the tides, 

 which differs in some respects from the lunar relations. 



The diurnal and semidiurnal tides are known to vary about 

 4 inches in an 8-feet tide. Then, supposing that 2 feet of the 

 8 feet is caused by solar attraction, the variation is one fifteenth 

 of the height due to lunar action. If the tide generated in deep 

 water is twelve lunar hours reaching a part of the coast, the greater 

 alternate twelve-hours' tide will become the lesser of the two. 

 There are many other considerations to take into account which 

 materially modify the size of the alternate tides at different parts 

 of the month ; and I do not put forward my own view with any 

 pretensions to improve the prediction of tides, which indeed is 

 already perfectly done by the machine invented by Sir W. 

 Thomson and Mr. E. Roberts of the Nautical Almanac Office, 

 What I wish to do is to give an explanation of a theory of the 

 tides which shall accord with the physical facts. Supposing 

 the point E is thirty diameters of the earth from the moon on 

 any day, then the point W will be 31. Then, the attraction 



* In the Admiralty Tide Tables there are only tides at ten places in the 

 Mediterranean recorded. The highest spring tide is 7 feet, and the ave- 

 rage 4*3 feet. Admiral Spratt, F.R.S., has just informed me that the 

 average of all spring tides in the Mediterranean is from 9 to 1 inches, 

 perceptible within three days of the highest tide. It is evident to me that 

 the tide in that sea is generated in basins, so that it is diffused in getting 

 to the coast, by which | of the proper height must be lost, 



