218 Mr. A. Tylor on Tides and Waves. 



names of the towns situated on the coast or river-bank in Plates 

 II. and III. 



In fig. 1, Plate II., a point is assumed in the Atlantic 300 

 miles from the Land's End, where the high- and low-water level 

 is assumed to be invariable, and where the mass of the ocean 

 water is supposed to move east and west very slowly in alternate 

 and opposite directions in each tide. 



When the flowing tide is moving a ship 3 miles an hour, there 

 is 360 miles difference in distance, and 6 hours' time, between 

 high water at Plymouth and Dover ; therefore the lost motion 

 is 18 miles out of 360, or 5 per cent. The impulse received at 

 Plymouth from the central slowly moving oceanic water must 

 have been transmitted through the deeper water at a much 

 higher rate, but only reaches Dover after travelling at 60 miles 

 an hour. Then the impulse is transmitted from Dover to Lon- 

 don at the rate of 120 miles in three hours, or 40 miles an hour, 

 the tide only taking a ship 9 miles in 3 hours; so that the lost 

 motion is 9 miles out of 120, or 7 per cent., the difference of 

 time between Plymouth and Dover (21 minutes) not being taken 

 into account. 



I have allowed a slope of 1 foot in Plates II. and III. to bring 

 the water to the mouth of the Clyde, and 5 feet to bring the water 

 to Palmouth from the Atlantic. 



If the level of the ocean were kept up above its due level only 

 2 inches between the western and eastern boundary of the 

 Atlantic deep water, that slope would suffice to create a current 

 of 3 feet per minute in the whole mass of deep water. This is 

 supposing the law of velocity followed the ratio I observe in 

 smaller cases. If the two inches were only water heaped up in 

 consequence of, or by the luni-solar attraction, it would create 

 no current at all while that attraction continued. 



As the effect of the moon on the oceanic water is only equal 

 to that of a sphere of 118*75 miles in diameter, equal in mean 

 density to the earth, placed near and revolving about C in a lunar 

 day, it occurred to me that some geological difficulties, such as 

 the evidence in the Crag and Quaternary deposits of the tides in 

 the Quaternary period being three or four times as large as at 

 present, might be explained by periodic changes of position 

 of part of the interior of the earth, rather than by supposing 

 great changes in the distance of the moon from the earth. Also 

 the quantity of water in the ocean can only be the difference 

 between that of the vapour held in the atmosphere or condensed 

 into snow or ice on the land, and the quantity of water or vapour 

 of water mechanically or chemically combined with the strata of 

 the earth. These are quantities capable of enormous variation in 

 geological periods under different conditions. There is also a 



