TIDES. 35 
to return towards B is equal to the tendency of the earth’s rotation to 
carry it towards c. The crests of the tide will under these circum- 
stances remain at # and ”, while the earth continues to rotate; and 
of course they will to us, inhabitants of the earth, seem to travel 
westward, just as the sun and stars seem to travel westward. The 
solar tide thus assumes the appearance of an immensely broad and 
excessively flat pair of waves travelling once round the earth from 
east to west every day. 
In the same way the attraction of the moon causes the lunar 
tide. The moon is so close to the earth—at a distance only 1-400th 
part of the distance of the sun—that, although the whole force of 
the moon’s attraction is small in comparison with the sun’s, there is 
a more sensible difference in the degree in which a body is attracted 
by the moon, according as the body is on the side of the earth next 
the moon or on the farthest side. And by going through the com- 
putation, it appears that the moon, on this account, produces a tide 
about two and a half times the height of the solar tide. 
Such is a picture of what would happen if the earth were covered 
everywhere by a deep ocean. But the phenomena are complicated 
upon the earth by the obstacle which continents present to the even 
advance of the tidal waves, and by the modifications which they 
undergo in shallow ‘or narrow seas, in which they rise to an exag- 
‘gerated height. 
The height of the tide varies in the different regions of the globe 
according to local circumstances. ‘The eastern coast of Asia and the 
western coast of Europe are exposed to extremely high tides ; while in 
the South Sea Islands, where they are very regular, they scarcely reach ° 
the height of twenty inches. On the western coast of South America, 
the tides rarely reach three yards; on the western coast of India 
they reach the height of six or seven ; and in the Gulf of Cambay it 
ranges from five to six fathoms. This great difference makes itself 
felt in our own and adjoining countries: thus, the tide which at 
Cherbourg is seven and eight yards high, attains the height of fourteen 
yards at Saint Malo, while it reaches the height of ten yards at 
Swansea, at the mouth of the Bristol Channel, increasing to double 
that height at Chepstow, higher up the river. In general, the tide 
is higher at the bottom of a gulf than at its mouth. 
The highest tide which is known occurs in the Bay of Fundy, 
which opens up to the south of the isthmus uniting Nova Scotia and 
New Brunswick. There the tide reaches forty, fifty, and even sixty 
feet, while it only attains the height of seven or eight in the bay to 
D2 
