176 HISTORY OF 



the same side of the globe ; because the moon's attraction, which 

 conspires with the earth's attraction, is there least. Now, 

 therefore, the waters farthest from the moon, having less weight, 

 and being lightest, will be pressed on all sides, by those that, 

 having more attraction, are heavier : they will be pressed, I say 

 on all sides ; and the heavier Vi^aters flowing in, will make them 

 swell and rise, in an eminence directly opposite to that on the 

 other side of the globe, caused by the more immediate influence 

 of the moon. 



In this manner the moon, in one diurnal revolution, produces 

 two tides ; one raised immediately under the sphere of its in- 

 fluence, and the other directly opposite to it. As the moon 

 travels, this vast body of waters rears upward, as if to watch its 

 motions; and pursues the same constant rotation. Howevei, 

 in this great work of raising the tides, the sun has no small 

 share; it produces its own tides constantly every day, just as 

 the moon does, but in a much less degree, because the sun is at 

 an immensely greater distance. Thus there are solar tides, and 

 lunar tides. When the forces of these two great luminaries 

 concur, which they always do when they are either in the same, 

 or in opposite parts of the heavens, they jointly produce a much 

 greater tide, than when they are so situated in the heavens, as 

 each to make peculiar tides of their own. To express the very 

 same thing technically ; in the conjunctions and oppositions of 

 the sun and moon, the attraction of the sun conspires with the 

 attraction of the moon ; by which means the high spring-tides are 

 formed. But in the quadratures of the sun and moon, the wnter 

 raised by the one is depressed by the other ; and hence thelowb. 

 neap-tides have their production. In a word, the tides are 

 greatest in the syzigies, and least in the quadratures. 



This theory well understood, and the astronomical terms pre 

 iously known, it may readily be brought to explain the various 

 appearances of the tides, if the earth were covered with a deen 

 sea, and the waters uninfluenced by shoals, currents, straits, or 

 tempests. But in every part of the sea, near the shores, the 

 geographer must come in to correct the calculations of the as- 

 tronomer. For, by reason of the shallowness of some places, 

 and the narrowness of the straits in others, there arises a great 

 diversity in the effect, not to be accounted for without an exact 

 knnvledge of all the circumstances ol the place. In the great 



