Page:Philosophical Transactions - Volume 003.djvu/6

 rising from the Neap to the highest Spring; and the like decrease of its height 'till Neap again is deducted.

3. The highest Menstrual Spring Tide is always the third Tide after the New or Full-Moon, if a cross Wind do not keep the Water out, as the North-east or North-west usually doth; whose contrary Winds, if strong, commonly make those to be High-Tides upon our Southern Coasts, which otherwise would be but low.

4. The highest Springs make the lowest Ebbs: (though I am inform'd by an expert Waterman, that it sometimes happens, that there may be a very low Ebb, though no high Spring, which they term an Out-let, or Gurges of the Sea; as when a great Storm chances off at Sea, and not on the Land.)

5. The Water neither flows nor ebbs: alike, in respect of equal degrees; but its Velocity increaseth with the Tide 'till just at Mid-water, that is, half flown, or at half Flood, at which time the Velocity is strongest, and so decreaseth proportionably 'till High-Water or Full-Sea. As may be guess'd at by the following Scheme, collected from my loose Papers, containing the Observations, as they were made at several times and places; which I rather set down as a standing proportion of degrees in the general, than to adequate every single Flux or Reflux so exactly as to half inches, or the like; but yet it may bear the odd minutes above six hours well enough. And it is farther to be noted, that although this be restained to Plymouth Haven, or the like, where the Water usually riseth about 16 Foot (I say usually, because it may vary in this Port from the lowest Neap to the highest Annual Spring above 7 or 8 Foot) yet it may indifferently serve for other paces, where it may rise as many fathom, or not so high, by a perpetual Addition or Subtraction. The