171- HISTOUY OF 



dually swells ; so that entering the mouths of rivers, it drives back 

 the river- waters to their heads. After a continual flux of six 

 hours, the sea seems to rest for a quarter of an hour ; and then 

 begins to ebb, or retire back again, from north to south, for six 

 hours more ; in which time the waters sinking, the rivers resume 

 their natural course. After a seeming pause of a quarter of an 

 hour, the sea again begins to flow as before : and thus it has 

 alternately risen and fallen, twice a-day, since the creation. 



This amazing appearance did not fail to excite the curiosity, 

 as it did the wonder of the ancients. After some wild conjec- 

 tures of the earliest philosophers, it became well known in the 

 time of Pliny, that the tides were entirely under the influence, 

 in a small degree, of the sun ; but in a much greater of the moon. 

 Jt was found that there was a flux and reflux of the sea, in the 

 space of twelve hours fifty minutes, which is exactly the time of 

 a lunar day. It was observed, that whenever the moon was in 

 the meridian, or, in other words, as nearly as possible over any 

 part of thd sea, that the sea flowed to that part, and made a tide 

 there ; on the contrary, it was found, that when the moon left 

 the meridian, the sea began to flow back again from whence i* 

 came ; and there might be said to ebb. Thus far the waters of 

 the sea seemed very regularly to attend the motions of the moon. 

 But as it appeared, likewise, that when the moon was in the 

 opposite meridian, as far off on the other side of the globe, that 

 there was a tide on tliis side also ; so that the moon produced 

 two tides, one by her greatest approach to us, and another by 

 her greatest distance from us : in other words, the moon, 

 in once going round the earth, produced two tides, always 

 at the same time; one on the part of the globe directly 

 under her ; and the other, on the part of the globe dii-ectly 

 opposite. 



Mankind continued for several ages conterit with knowing the 

 general cause of these wonders, hopeless of discovering the par- 

 ticular manner of the moon's operation. Kepler was the first 

 who conjectured that attraction was the principal cause ; assert, 

 ing, that the sphere of the moon's operation extended to the 

 earth, and drew up its waters. The precise manner in which 

 this is done, was discovered by Newton. 



The moon has been found, like all the rest of the planets, to 

 attract and to be attracted by the earth. This attraction pre- 



