(4R) 
the Moon, wherein ihe approaches nearefl: either to tfic 
Zenith or Nadir of the place : whence it is that the 
Moon in the Northern Signs, in this part of the World, . 
maices the greateft Tides when above the Earth, and in 
Southern Signs, when under the Earth,- the EltedJ: be- 
ing always tde greateft where the Moon is fartheft from 
the Horizon, either above or below it. And this alter- 
nate increaleand decreafe of the Tides has been obferv* 
ed to hold true on the Coaft of Englaniy at Er 'tftol by 
Capt. Sturmy, and at Plymouth by Mr. Colepreffe. 
But the Motions hitherto mentioned are lomewhat al- 
tered by the Libration of the Water, whereby, tho' 
the Aftion of the Luminaries fliould ceafe, the Flux 
and Reflux of the Sea would for fome time continue : 
This Conftrvation of the imprefled Motion diminiflies 
the differences that otherwife would be between two 
conftquent Tides, and is the reafon why the higheft 
Spring Tides are not precifely on the new and full 
Moons, nor the Neaps on the Quarters; but general- 
ly they are the third Tides after them, and fometimes 
later. 
All thefe things would regularly come to paft, if the 
whole Earth were covered with Sea very deep; but by 
reafon of the (hoalnefs of fome places, and the narrow- 
nefs of the Streights, by which the Tides are in many 
eafes propagated, there arifes a great diverfity in the Er- 
fed:, and not to be accounted for, without an exacS: 
Knowledge of all the Circumftances of the Places, as 
of the Pofition of theLmd, and the Breadth and Depth 
of the Channels by which the Tide flows ; for a very- 
flow and imperceptible Motion of the whole Body of 
the Water, where it is. (for example} a Miles deep^. 
will fuffice to raile its Surface l o or ix Feet in a Tides 
time ; whereas, if the fame quantity of Water were to 
be conveyed upon a Channel of 40 Fathoms deep, it 
would 
