About the Tydes. 31

About the Tydes.

of the Heavens; but this general Rule is only true under the Poles, where the Equinoctial and Horizon are the same. And it also supposeth, that the Departure of the Moon from the Sun were at all times equal; in both which respects the Rule is defective.

For at London, (which lies in 51 Degrees 30 Minutes of North Latitude) where a South- West or a North-East Moon makes a full Sea, or High Water; and that is at Three of the Clock, (and this is true, when the Moon is in either of the Equinoctial Signs Aries, or Libra, or near thereunto, and hath no Latitude) but in the same Place, (viz. London) the Moon being in Cancer, and having 5 Degrees of North Latitude, it will be 30 Minutes after Ten of the Clock before the Moon will be at North-East, which should be at Nine of the Clock by the vulgar Rule, which is an Hour and a half too late: And the same Day she will be South-West at half an hour after One, which is an hour and half too soon.

Now to correct this Error, and to prove the true Time of High Water at Londonbridge, it will be best performed by knowing the Day of the New or Full Moon, which every Almanack will acquaint you with; for upon the Day of the New or Full Moon, it will be High Water at Londonbridge at Three of the Clock, and every Day after at such Hours and Minutes as this Table doth shew.

The former Error amended.


The TYDE TABLE.

 


  Ho.Min.
 New Moon.
Full Moon.
300
Days after the New, or Full Moon.1Time of High Water at London.348
2431
3514
4552
5630
673
7736
8824
9927
101030
111128
121226
13119
14212

This Table needs not much explaining the Use thereof; for if you look for any Day in the Year in your Almanack, you may quickly count how many Days are past since the last New or Full Moon, then find that Number in the first Column of this Table; and right against it in the second, you have the Hour and Minute that it will be High Water at London Bridge that Day. So if you should find in your Almanack any Day to be 5 Days after the New or Full Moon, look for 5 in the first Column, and right against it stands 6 Hours and 30 Minutes; and at that time it will be High Water at London Bridge. But here you are to take notice, that there is a considerable Difference between the Spring Tydes and the Neap Tydes, in respect of Time; for the Neap Tydes will be sometimes an Hour or more sooner than the Table gives them to be, as hath been before taken notice of, and shall be made more manifest by what follows.

The Use of this Table.

Difference betwixt Spring and Neap Tydes.


Of the Tydes in the River of Thames.

 

There are in this River Three Things worthy to be observed, viz. Its Spring Tydes, its Overflowing its Banks, and its strange shifting of Tydes at some times; touching all which, I shall deliver the Conceptions of two Learned Philosophers of our Age. And first,

3 things observable in the Thames.


Of Spring Tydes.

 

These Tydes are higher than ordinary, and do happen about every Full and Change of the the Moon. The great French Philosopher Des Cartes endeavours to give us the Reason of it, telling us, that from the Theorique of the Moon, that the Moon moves so in her Eliptical Orb about the Earth, that at her Full and Change she comes nearer to the Earth, and in each Quarter goes further from it. Whence (from this Hypothesis) greater Tydes must be at the Full and Change; and Neap or Low Tydes at the Quarters; all which, for the most part, is true indeed; and without doubt the Moon's Nearness at the Full and Change is the Cause of the Spring Tydes, even as the Moon's being further off at the Quarters makes then the Neap Tydes.

Spring Tydes.

Greater Tydes at the New and Full Moons.

Neap Tydes at the Quarters.

But there is another thing considerable (says another Philosopher) in the business, which Des Cartes doth not consider, or it may be, did not know; that is, that the Spring Tydes in our River of Thames come not just upon the Full or Change, but two or three Days after, and the like doth the Neap Tydes after the Quarters; which is against his Hypothesis. Therefore to untye this Knot; I conceive the Cause why the Spring Tydes are at the highest two or three Days after the Full and Change, and not on the very Day, is the same with that, why the sharpest pinching Time of Winter comes not just in the shortest Day, when the Sun is at the lowest with us, but in January, and about four or five Weeks after: Why also the coldest Time of the Night is not at Midnight, but about Break of Day. Why the hottest Time in summer is in July, 4 or 5 Weeks after the Solstice; and why the hottest time of the Day is not just at Noon, but about Two or Three of the Clock in the Afternoon.

Mr. Childrey.

The Reasons about the High Tydes not being at Full or New Moons.

Why the coldest time is not at the shortest Day; and the hottest not at the longest.

To demonstrate the Reason of this, he saith, Let us suppose a large Cistern, having a Cock at (or towards) the Bottom of it, that constantly lets out Six Gallons of Water in a certain space of Time; and over the Cistern, suppose another Cock that conveys Water from some other Place into this Cistern, and which runs at first but very slow, but after by Degrees faster and faster, until at last it lets in 8 Gallons in the same Space of Time that the Cock below lets out 6 Gallons. And farther, let us suppose, that the Cock above, after it hath continued running for some space of Time after the Rate of 8 Gallons, doth decrease by the same Degrees (that before it increased by) to 7 Gallons, and so to 6, 5, 4, and so less and less, until at length it quite gives over running. There is no Man, I think, but will say, that this Cistern will be fuller of Water, when it hath decreased it from 8 Gallons in a Space to 7 Gallons; and yet fuller when it is decreased to 6 Gallons and a half, than when it was at 7; and fullest of all just before is decreased to 6 Gallons in a Square; because till that time there comes more Water into the Cistern at the Cock than, there goes at the other.

An Experiment to explain this Resaon.

Even so, though the Heat of the Sun, simply considered in it self, be not so great about the Middle of July, as to the Solstice in June, because he is descended lower; yet because the Heat that the Sun sends forth in the Air every Day, is greater than the Cold which his Absence causeth by Night, nothing can follow thereupon but an Increase of the Heat. And the like may be said of Afternoon Heats, January after Winters, Morning Colds, and of Spring Tides, coming behind the Full Moons, and the Changes.


Of the Overflowing of the Banks.

 

The Thames overflowing its Banks, proceedeth from several Causes.

First, From great Rains, whereby the fresh Waters raise up the River, and going down to the Sea are stopt by the Floods, whence they must needs swell above their usual Height. Of this there was a notable Example in the Year 1555,

The Cause of the Thames overflowing.

where