THE TIDES. 



THE phenomena of the tides of the ocean are too remarkable and important 

 to the social and commercial interests of mankind, not to have attracted notice 

 at an early period in the progress of knowledge. The intervals between the 

 epochs of high and low water everywhere corresponding with the intervals be- 

 tween the passage of the moon over the meridian above and below the horizon, 

 suggested naturally the physical connexion between these two effects, and in- 

 dicated the probability of the cause of the tides being found in the motion of 

 the moon. 



KEPLER developed this idea, and demonstrated the close connexion of these 

 phenomena ; but it was not until the theory of GRAVITATION was established 

 by Newton, and its laws fully developed, that all the circumstances of the tides 

 were clearly explained, and shown incontestably to depend on the influence of 

 the sun and moon. 



There are few subjects in physical science about which there prevail moie 

 erroneous notions among those who are but a little informed, than with re- 

 spect to the tides. A common idea is, that the attraction of the moon draws 

 the waters of the earth toward that side of the globe on which the moon hap- 

 pens to be placed, and that consequently they are heaped up on that side, so 

 that the oceans and seas acquire there a greater depth than elsewhere ; and 

 thus it is attempted to be established that high water will take place under, or 

 nearly under, the moon. But this neither corresponds with the fact, nor, if it 

 did, would it explain it. High water is not produced merely under the moon, 

 but is equally produced upon those parts most removed from the moon. Sup- 

 pose a meridian of the earth so selected, that, if it were continued beyond the 

 earth, its plane would pass through the moon ; then we find that, subject to cer- 

 tain modifications, a great tidal wave, or what is called htgh water, will be formed 

 on both sides of this meridian ; that is to say, on the side next the moon, and 

 on the side remote from the moon. As the moon mores in her monthly course 

 round the earth, these two great tidal waves follow her. They are, of 



