T 1 D 



The greater the rise of high water above the level of a fixed point, the 

 greater is the depression of the corresponding low water relatively to the 

 same point. 



The height of the tide is affected by the vicinity of the moon to the 

 earth, and increases, caeteria paribus, when the parallax and apparent 

 diameter of the moon increase, but in a higher ratio. 



The rise of the tide is affected by the declination of the luminaries j it 

 is greatest, caeteris paribus, at the equinoxes, and least at the solstices. 



When the moon is in the northern signs, the tide of the day, in all 

 northern latitudes, is somewhat greater than the tide of the night : and 

 the contrary when the moon is in the southern signs. 



If the tides he considered relatively to the whole earth, and to the 

 open eea, there is a meridian about SO*' eastward of the moon, where it 

 is always high water; on the west side of this circle, the tide is flow- 

 ing; on the east, it is ebbing ; and on the meridian, at right /'a to the 

 game, it is every where low water. 



In high latitudes, whether south or north, the rise and fall of the tid 

 ire inconsiderable. It is probable that at the poles there are no tidea. 



The tides, in narrow seas, and on shores far from the main body of 

 the ocean, are not produced in those seas by the direct action of the lu- 

 minaries, but are waves propagated from the great diurnal undulation, 

 and moving with much less velocity. For instance, the high water 

 transmitted from the tide in the Atlantic, reaches Uahant between three 

 nnd four hours after the moon has parsed the meridian. This wave then 

 divides itself into three; one passing up the British Channel, another 

 ranging along the west side of Ireland and Scotland, and the third en- 

 tering the Irish Channel. The first of these flows thrmigh the channel 

 at about 50 miles as hour, and reaches the Nore about 12 at night The 

 second moves more rapidly, so as to reach the North of Ireland by six, 

 and the Orkneys by nine, and the Naze of Norway by 12 ; and in 12 

 hours more it reaches the Nore, where it meets the morning tide, that 

 left the mouth of the channel only eight hours before. Thus these two 

 tides travel round Britain in about 18 hours, in which time the primi- 

 tive tide has gone round the whoio circumference of the earth and nearly 

 45 degree* more. 



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