VOL. I.] PHILOSOPHICAL TRANSACTIONS. 99 



But the true inequality of the natural days, arising from a complication 

 of those two causes, sometimes crossing and sometimes promoting each other, 

 though we should find some increases or decreases of the natural days at all 

 those seasons answerable to the respective causes, and perhaps of tides propor- 

 tionably thereunto, yet the longest and shortest natural days absolutely of the 

 whole year, arising from this complication of causes, are about those times of 

 Allhallondtide and Candlemas, about which those annual high tides are found to 

 be; as will appear by the tables of equation of natural days. And therefore I 

 think we may with very good reason cast this annual period upon that cause, 

 or rather complication of causes. For, as we before showed in the menstrual 

 and diurnal, there will, by this inequality of natural days, arise a physical acce- 

 leration and retardation of the earth's mean motion, and accordingly a casting 

 of the waters backward or forward, either of which will cause an accumulation 

 or high water. 



It is true, that these longest and .shortest days do fall rather before than after 

 Allhallondtide and Candlemas, to wit the ends of October and January; but so 

 do also sometimes those high tides : and it is not yet so well agreed amongst 

 astronomers what are all the causes, and in what degrees, of the inequality of 

 natural days, but that there be diversities among them, about the true time : 

 and whether the introducing of this new motion of the earth in its epicycle 

 about this common centre of gravity, ought not therein also to be accounted 

 for, I will not now determine ; having already said enough, if not too much, 

 for the explaining of this general hypothesis, leaving the particularities of it to 

 be adjusted according to the true measures of the motions; if the general hypo- 

 thesis be found fit to be admitted. 



Yet this I must add, that whereas I cast the time of the daily tides to be at 

 all places when the moon is there in the meridian ; it must be understood of 

 open seas, where the water hath such free scope for its motions, as if the whole 

 globe of earth were equally covered with water; well knowing that in bays 

 and inland channels, the position of the banks, and other like causes, must 

 needs make the times to be much different from what we suppose in the open 

 seas; and likewise, that even in the open seas, islands and currents, gulfs and 

 shallows, may have some influence, though not comparable to that of bays and 

 channels. And moreover, though I think that seamen do commonly reckon 

 the time of high water in the open seas to be when the moon is there in the 

 meridian, as this hypothesis would cast it ; yet I do not take myself to be so 

 well furnished with a history of tides, as to assure myself of it, much less to 

 accommodate it to particular places and cases. 



Having thus dispatched the main of what I had to say concerning the sea's 



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