Philosophical Transactions of the Royal Society Part 31

_Observations made in several places, Of the late _Eclipse of the Sun_, which hapned on the 22 of _June_, 1666._

The Observations that were made at _London_ by Mr. _Willughby_, Dr. _Pope_, Mr. _Hook_, and Mr. _Philips_, are these:

The Eclipse began at 5h. 43' h. '

{ 3/11 diam. at 6. 00 | 5 dig. at 7. 06 { 4 digits at 6. 07 | 4 dig. at 7. 13 It was { 5 dig. at 6. 13 | 3 dig. at 7. 20 darkned,{ 6 dig. at 6. 21 | 2 dig. at 7. 26 { 7 dig. at 6. 39 | 1 dig. at 7. 32 { 6 dig. at 6. 57 | 0 dig. at 7. 37

Its _Duration_ hence appears to have been one hour and 54 m. Its _greatest Obscurity_ somewhat more than 7. digits. About the middle, between the Perpendicular and Westward Horizontal _Radius_ the Sun, viewing it through Mr. _Boyle_'s 60. foot-_Telescope_, there was perceived a little of the Limb of the Moon without the Diske of the Sun: which seemed to some of the Observers to come from some s.h.i.+ning _Atmosphere_ about the Body either of the Sun or Moon.

They affirm to have observ'd the _Figure_ of this _Eclipse_, and measured the {296} _Digits_, by casting the _Figure_ through a 5 foot _Telescope_, on an extended paper, fix't at a certain distance from the Eye-gla.s.se, and having a round figure; all whose _Diameters_ were divided, by 6 _Concentrick_ Circles, into 12 _Digits_.

The Observations made at _Madrid_ by a n.o.ble Member of the _Royal Society_, His Excellence the Earle of _Sandwich_, as they were sent to the Right Honourable, the Lord Vice-Count _Brounker_, are these;

The Eclipse _began_ at _Madrid_ about 5 of the Clock in the morning, at 5 h. 15', the Suns _Alt.i.tude_ was 6 deg. 55'.

The _Middle_ of it was at 6 h. 2', the Suns _Alt.i.tude_, 15. deg. 5'.

The _End_ was exactly at 7 h. 5'; the Suns _Alt.i.tude_, 25. deg. 24'.

The _Duration_, 2h. 4'.

37. Parts of the Suns diameter remained light.

63. Parts of the same were darkened.

The Observations made at _Paris_ by Monsieur _Payen_, a.s.sisted by several _Astronomers_, as they were printed in _French_, and addressed to Monsieur de _Montmor_, are these;

The _Eclipse_ began there, at 5 h. 44'. 52". _mane_. It ended at 7 h. 43'.

6". So that its _whole Duration_ was 1 h. 58'. 14". The _greatest Obscuration_ they a.s.sign to have been 7. dig. 50. m. but they adde, that it seem'd to have been greater by 3 minuts; which M. _Payen_ imputes to a particular motion of _libration_ of the Suns Globe, which entertain'd that Luminary in the same _Phasis_ for the s.p.a.ce of 8. _min._ and some _seconds_, as if it had been stopped in the midst of its Course; rather than to a tremulous Motion of the _Atmosphere_, as _Scheiner_ would have it.

They intimate that they took the time of each _Phasis_ from half _digit_ to half _digit_, as well by a _Pendulum_, as by the _Alt.i.tudes_ of the _Suns Center_ above the _Horizon_, corrected by the _Verticall Paralaxes_ and _aestivall Refractions_, by which they judged, that though the Time by the _Pendulum_ may be sufficient for _Mechanicall_ Operations, yet 'tis not exact enough for establis.h.i.+ng the _Grounds of true Astronomy_.

They further conceive that the apparent _Diameters_ were almost equal; seeing that in the _Phasis_ of 6. _Digits_, the _Circ.u.mference_ of the _Moons disk_ pa.s.sed through the _Center_ of that of the _Sun_, so as that two Lines drawn through the two _Horns_ of the Sun, made with the _Common Semi-diameter_ two _Equilateral Triangles_.

Next, they affirm, That there was so great a Variation in the _Parallaxes_, by reason as well of the Refractions of the Air, which environs the Earth, as of the Alteration of the Air, which encompa.s.ses the Moon, that the _Horns_ of the Sun, there formed by the Shaddow of the Moon, appeared in all kinds of _Figures_; Sometimes inclined to the _Vertical_, sometimes _Perpendicular_ to the _Horizon_, and at last _Parallel_; the _Convexe_ part respecting the _Heaven_, and the _Concave_, the _Horizon_. By the crossing (_so they go on_) of the {297} _Horns_ with the _Angles of Inclination_, it will be easie to those, that have exactly observed them, and that are skill'd in the higher _Astronomical_ Calculations, to compute the _true Place_ of the _Moon_ in her _Orbite_, that so it may be compared with that of the _Tables_, and with that, which has been observ'd in other places, for the more precise determinating of the _Difference_ of _Meridians_ (that being the way, esteem'd by _Kepler_ the most certain) and for making a good Judgment of the defect or exactnesse of the Celestial _Tables_.

Then they observe, That the _Beginning_ and the _Middle_ of this _Eclipse_ hapned to be in the _North Eastern Hemisphere_, and the _End_, in the _South-Eastern_. The _first Contact_ (as 'twere) of the two Disks was observ'd in the _Superior Limb_ of the _Suns Disk_ in respect to the _Vertical Line_, and in the _Inferior_ in respect to the _Ecliptick_: But the _Middle_, and the _End_ were seen in the _Superior Limb_, in respect both to the _Vertical_ and the _Ecliptick_: And (what to this Author seems extraordinary) both the _Beginning_ and the _End_ of this _Eclipse_ hapned to be in the _Oriental_ part of the Suns Disk.

Lastly, they take notice, that by their Observations it appears, that there is but little exactness in all the _Astronomical Tables_, predicting the _Quant.i.ty_, _Beginning_ and _Duration_ of this Eclipse; Those of _Lansbergius_ importing, That the Obscuration should be of 10. dig. 48'; those of _Ricciolo_, of 9. dig. 1'; and those of _Kepler_, of 7. dig. 30'.

16": Again, that the _Duration_ should be of 2h. 2'. Lastly, The _Beginning_ did antic.i.p.ate the _Ricciolan Tables_ by 5 _minuts_, the _End_ by 23; and the _Middle_, almost by 11. In the mean time the Author notes, that the _Rudolphin Tables_ come nearest to the Truth; and withal a.s.sures the _Reader_ of the goodnesse of the _Instruments_ employed in his _Observations_, and of the singular care, he, together with his skilful a.s.sistants, took in making them.

_Some Inquiries and Directions concerning _Tides_, proposed by Dr.

_Wallis_, for the proving, or disproving of his lately publish't _Discourse_ concerning them_.

The Inquisitive Dr. _Wallis_, having in his lately printed _Hypothesis_ of Tides intimated, that he had reason to believe, that the _Annual Spring-tides_ happen to be rather about the beginnings of _Febr._ and _Nov._ than the two _aequinoxes_, doth in a late Letter to the _Publisher_, written from _Oxford_ in _Aug._ last, desire, that some understanding Persons at _London_, or _Greenwich_, but rather nearer the Sea, or upon the Sea-sh.o.r.e, would make _particular_ Observation of all the _Spring-Tides_ (_New-Moon_ and _Full-Moon_) between this and the End of _November_; and take account of the _Hour_, and of the _Perpendicular height_: that we may see, whether those in _September_, or those of _November_ be highest: And it were not amiss, the Low waters were observed too. Which may be easily done by a mark made upon any standing Post in the Water, by any {298} Water-man, or other understanding Person, who dwells by the Water-side.

It would also deserve (thinks he) to be inquired into, whether, when the Tides be highest, the Ebbs be ever lowest, & _contra_; (which is generally affirmed, and almost put out of question) or rather (which sutes best with this _Hypothesis_) whether, when the Tides are highest, both in the _Annual_ and _Menstrual_ Periods, the Low waters be not also highest; and at Neap Tides, the Ebbes also very low.

He adds, that he should expect, that the Spring Tides now coming, and those at the beginning of _September_, should not be so high, as those at the _middle_ of _September_; and then lower again at the _beginning_ of _October_, and after that, higher at the _middle_ of _October_, and higher yet about the _beginning_ of _November_ (at the usual times of _Spring-tides_ after the _New_ and _Full_.)

_Considerations and Enquiries concerning _Tides_, by Sir _Robert Moray_; likewise for a further search into Dr. _Wallis's_ newly publish't _Hypothesis_._

In regard that the High and Low waters are observed to increase, and decrease regularly at several seasons, according to the Moons age, so as, about the _New_ and _Full Moon_, or within two or three daies after, in the Western parts of _Europe_, the _Tides_ are at the _highest_, and about the _Quarter-Moons_, at the _lowest_, (the former call'd _Spring-tides_, the other _Neap-tides_;) and that according to the height and excesses of the _Tides_, the _Ebbes_ in opposition are answerable to them, the heighest Tide having the lowest Ebbe, and the lowest Ebbe, the highest Tide; the Tides from the _Quarter_ to the _highest Spring-tide_ increasing in a certain proportion; and from the _Spring tide_ to the _Quarter-tide_ decreasing in like proportion, as is supposed: And also the _Ebbes_ rising and falling constantly after the same manner: It is wished, that it may be inquired, in what proportion these Increases and Decreases, Risings and Fallings happen to be in regard of one another?

And 'tis supposed, upon some Observations, made in fit places, by the above-mentioned Gentleman, though, (as himself acknowledges) not thoroughly and exactly performed, that the Increase of the Tides is made in the _Proportion_ of _Sines_; the first Increase exceeding the lowest in a small proportion; the next in a greater; the third greater than that; and so on to the mid-most, whereof the excess is greatest, diminis.h.i.+ng again from that, to the highest Spring-Tide; so as the proportions, before and after the _Middle_, do greatly answer one another, or seem to do so. And likewise, from the _highest Spring-tide_, to the _lowest Neap-tide_, the _Decreases_ seem to keep the like proportions; the _Ebbes_ rising and falling in like manner and in like proportions. All which is supposed to fall out, when no Wind or other Accident causes an alteration. {299}

And whereas 'tis observed, that upon the main Sea-sh.o.r.e the Current of the Ebbings and Flowings is sometimes swifter, and sometimes slacker, than at others, so as in the beginning of the Floud the Tide moves faster but in a small degree, increasing its swiftness constantly till towards the _Middle_ of the Floud; and then decreasing in velocity again from the _Middle_ till to the top of the High water; it is supposed, that in Equal s.p.a.ces of Time, the Increase and Decrease of velocity, and consequently the degrees of the Risings and Fallings of the same, in Equal s.p.a.ces of time, are performed according to the _Proportion_ of _Sines_.

But 'tis withall conceived, that the said _Proportion_ cannot hold _exactly_ and _precisely_, in regard of the _Inequalities_, that fall out in the _Periods_ of the _Tides_, which are commonly observed and believed to follow certain _Positions_ of the _Moon_ in regard of the _Equinox_, which are known not to keep a _precise_ and _constant_ Course: so that, there not intervening equal portions of Time between one New Moon and another, the Moons return to the same _Meridian_, cannot be alwaies perform'd in the same Time; and consequently there must be a like Variation of the Tides in the Velocity, and in the Risings and Fallings of the Tides, as to equal s.p.a.ces of time. And the Tides from New-moon to New-moon being not alwaies the same in number, as sometimes but 57, sometimes 58, and sometimes 59, (without any certain order of succession) is another evidence of the difficulty of reducing this to any great exactness. Yet, because 'tis worth while, to learn as much of it, as may be, the _Proposer_ and many others do desire, That Observations be constantly made of all these Particulars for some Months, and, if it may be, years together. And because such Observations will be the more easily and exactly made, where the Tides rise highest, it is presumed, that a fit _Apparatus_ being made for the purpose, they may be made about _Bristol_ or _Cheap-stow_, best of any places in _England_, because the Tides are said thereabout to rise to ten or twelve fathoms; as upon the coast of _Britanny_ in _France_, they do to thirteen and fourteen.

In order to which, this following _Apparatus_ is proposed to be made use of. In some convenient place upon a Wall, Rock, or Bridge, &c. let there be an _Observatory_ standing, as neer as may be to the brink of the Sea, or upon some wall; and if it cannot be well placed just where the Low water is, there may be a Channel cut from the Low water to the bottom of the Wall, Rock, &c. The Observatory is to be raised above the High water 18. or 20. foot; and a Pump, of any reasonable dimension, placed perpendicularly by the Wall, reaching above the High water as high as conveniently may be.

Upon the top of the Pump a Pulley is to be fastned, for letting down into the Pump a piece of floating wood, which, as the water comes in, may rise and fall with it. And because the rising and falling of the water amounts to 60. or 70. foot, the Counterpoise of the weight, that goes into the Pump, is to hang upon as many Pulleys, as may serve to make it rise & fall within the s.p.a.ce, by which the height of the Pump exceeds the height of the Water. And because by {300} this means the Counterpoise will rise and fall slower; and consequently by less proportions, than the weight it self, the first Pulley may have upon it a Wheele or two, to turn _Indexes_ at any proportion required, so as to give the minute parts of the motion, and degrees of risings and fallings. All which is to be observed by _Pendulum-watches_, that have _Minutes_ and _Seconds_, with _Checks_, according to Mr. _Hugens's_ way.

And because if the Hole, by which the water is let into the Pump, be as large as the Bore of the Pump it self, the weight that is raised by the water, will rise and fall with an Undulalation, according to the inequality of the Sea's Surface, 'twill therefore be fit, that the Hole, by which the water enters, be less than half as bigg as the Bore of the Pump; any inconvenience that may follow thereupon, as to the Periods and Stations of the Floud and Ebb, not being considerable.

And to the end, that it may appear the better; what are the _particular_ Observations, desired to be made, near _Bristol_ or _Cheap-stow_ bridg, it was thought not amiss, to set them down distinctly by themselves.

1. The degrees of the Rising and Falling of the water every quarter of an hour (or as often as conveniently may be) from the Periods of the Tides and Ebbs; to be observed night and day, for 2 or 3 months.

2. The degrees of the velocity of the Motion of the Water every quarter of an hour for some whole Tides together; to be observed by a second _Pendul_-watch: and a logg fastened to a line of some 50 fathoms, wound about a wheel.

3. The exact measures of the Heights of every utmost High-water and Low-water, from one Spring-tide to another, for some Months or rather Years.

4. The exact Heights of Spring-tides and Spring-Ebbs for some Years together.

5. The Position of the Wind at every observation of the Tides; and the times of its Changes; and the degrees of its Strength.

6. The State of the Weather, as to Rain, Hail, Mist, Haziness, &c, and the times of its Changes.

7. At the times of observation of the Tides, the height of the _Thermometer_; the height of the _Baroscope_; the height of the _Hygroscope_; the Age of the Moon, and her _Azimuths_; and her place in all respects; And lastly the _Sun's_ place; all these to _minutes_.

And it would be convenient, to keep _Journal Tables_, for all these Observations, each answering to its day of the Month.

For the _Apparatus_ of all these observations, there will be particularly necessary.

A good _Pendulum_-watch.

A _Vane_ shewing _Azimuths_ to minute parts.