Chapter 14

Besides that Transient Shadow last mentioned, there hath been observed, by Monsieur _Cassini_, a permanent Spot in the Disque of _Jupiter_; by the help whereof, he hath been able to observe, not onely that _Jupiter_ turns about upon his own Axis, but also the Time of such conversion; which he {144} estimates to be, 9 hours and 56 minutes.

For as _Kepler_ did before conjecture, from the motion of the Primitive Planets about the Sun as their Center, that the Sun moved about its own Axis, but could not prove it, till by _Galileo_ and _Shiner_ the Spots in the Sun were discovered; so it hath been thought reasonable, from the Secundary Planets moving about _Jupiter_, that _Jupiter_ is also moved about his Axis; yet, till now, it hath not been evinced by Observation, That it doth so move; much less, in what Period of Time. And the like reason there is to judge so of _Saturn_, because of the Secundary Planet discovered by Monsieur _Hugens de Zulichem_ to move about it; (though such motion be not yet evinced from Observation:) as well as that of the _Earth_, from its Attendant the _Moon_.

Whether the same may be also concluded of the other Planets, _Mars_, _Venus_, and _Mercury_, (about whom have not yet been observed any Secondary Planets to move,) is not so evident. Yet there may be somewhat of like probability in those. Not onely, because it is possible they may have Secundary Planets about them, though not yet discovered; (For, we know, it was long after those of _Jupiter_, before that about _Saturn_ was discovered; and who knows, what after times may discover about the rest?) But because the Primary Planets being all in like manner inlightned by the Sun, and (in all likely hood) moved by it; it is likely that they be moved by the same Laws and Methods; and therefore, turn'd about their own Axis, as it is manifest that some of them are.

But, as for the Secundary Planets, as well those about _Jupiter_, as that about _Saturn_; it is most likely that they have no such Rotation upon their Axis. Not so much because, by reason of their smalness, no such thing hath been yet observed, (or, indeed, could be, though it were true;) But because they being Analogical to our _Moon_, it is most likely that they are moved in like manner. Now, though it be {145} true, that there is some kind of _Libration_ of the Moon's body, so that we have not precisely just the same part of it looking towards us; (as is evident by _Hevelius_ observations, and others;) yet is there no Revolution upon its Axis; the same part of it, with very little alteration, always respecting us, as is to be seen in _Hevelius_ his Tratise _de Motu Lunæ Libratorio_, and indeed, by all those who have written particularly of the spots on the Moon; and is universally known to all that have with any curiosity viewed it with Telescopes.

* * * * *

_Of some Philosophical and curious Books, that are shortly to come abroad._

1. Of the _Origine_ of _Forms_ and _Qualities_, deduced from _Mechanical_ Principles; by the Honorable _Robert Boyle_ Esq.

2. _Hydrostatical Paradoxes_, by the same. Both in _English_.

3. A Tract of the _Origine_ of the _Nile_, by Monsieur _Isaac Vossius_, opposed to that of Monsieur _de la Chambre_, who is maintaining, That _Niter_ is the principal cause of the Inundation of that River.

4. A Dissertation of _Vipers_, by _Signor Redi_, an _Italian_.

5. A Discourse of the _Anatomy_ of _a Lyon_, by the same.

6. Another, _De Figuris Salium_, by the same.

7. A Narration of the Establishment of the _Lyncei_, an _Italian_ Academy, and of their Design and Statutes: the Prince _Cesi_ being the Head of them, who did also intend to establish such Philosophical Societies in all parts of the World, and particularly in _Africa_ and _America_, to be by that means well informed of what considerable productions of Nature were to be found in those parts. The Author yet _Anonymus_.

8. To these I shall add, a Book newly Printed in _Oxford_ (and not yet dispersed) being, _A Catalogue of Fixed Stars_ with their _Longitudes, Latitudes, and Magnitudes_, according to the _Observations_ of _Uleg-Beig_ (a King, and famous Astronomer, who was _Great-Grand-childe_ to the famous {146} _Tamerlane_, and one of his Successors in some of his Kingdoms) made at _Samarcand_, his cheief seat, (for the year of the Hegira 841, for the year of Christ 1427), who not finding the _Tables_ of _Ptolemy_ to agree sufficiently with the Heavens, did with great diligence, and expense, make observations anew; as _Tycho Brahe_ hath since done. It is a small part of a larger _Astronomical Treatise_ of his, whereof there be divers _Persian_ Manuscript Copies in _Oxford_. Out of which this is Translated and Published, both in _Persian_ and _Latine_, by Mr. _Thomas Hyde_, now Library Keeper to the _Bodleyan_ Library in _Oxford_: (with Commentaries of his annexed:) Like as another part of it hath formerly been by Mr. _John Graves_. And it were a desirable work that the whole were Translated, that we might be the better acquainted with what was the Eastern Astronomy at that time.

* * * * *

_Published with License._

Oxford, Printed by _A: & L: Lichfield_, for _Ric: Davis_. 1666.

{147}

* * * * *

_Num._ 9.

PHILOSOPHICAL _TRANSACTIONS._

* * * * *

_Munday_, _Feb._ 12. 1665/6.

* * * * *

The Contents.

_An _Apendix_ to the _Directions_ for Seamen, bound for far voyages. Of the judgment of some of the _English_ Astronomers, touching the difference between two learned men, about an Observation made of the first of the two late _Comets_. Of a _Correspondency_, to be procured, for the finding out of the _True_ distance of the _Sun_ and _Moon_ from the Earth. Of an Observation not long since made in _England_ of _Saturn_. An Account of some _Mercurial_ Observations, made with a _Barometer_, and their Results. Some Observations of _Vipers_, made by an _Italian_ Philosopher._

* * * * *

_An _Appendix_ to the _Directions_ for Seamen, bound for far Voyages._

Whereas it may be of good use, both _Naval_ and _Philosophical_, to know, both how to sound depths of the sea _without a Line_, and to fetch up water from any depth of the same; the following waies have been contrived by Mr. _Hook_ to perform both; (which should have been added to the lately printed _Directions for Seamen_, if then it could have been conveniently done.) {148}

_First_, for the sounding of depths without a Cord, consider _Figure_ 1, and accordingly take a Globe of _Firr_, or _Maple_, or other light Wood, as A: let it be well secured by Vernish, Pitch, or otherwise, from imbibing water; then take a piece of Lead or Stone, D, considerably heavier then will sink the Globe: let there be a long Wire-staple B, in the Ball A, and a springing Wire C, with a bended end F, and into the said staple, press in with your fingers the springing Wire on the bended end: and on it hang the weight D, by its ring E, and so let Globe and all sink gently into the water, in the posture represented in the first _Figure_, to the bottom, where the weight D touching first, is thereby stopt; but the Ball, being by the _Impetus_, it acquired in descending, carried downwards a little after the weight is stopt, suffers the springing wire to fly back, and thereby sets it self at liberty to reascend. And, by observing the time of the Ball's stay under water (which may be done by a Watch, having minuts and seconds, or by a good Minut-glass, or best of all, by a Pendulum vibrating seconds) you will by this way, with the help of some _Tables_, come to know any depth of the sea.

Note, that care must be had of proportioning the weight and shape of the Lead, to the bulk, weight, and figure of the Globe, after such a manner, as upon experience shall be found most convenient.

In some of the Tryals already made with this Instrument, the Globe being of Maple-wood, well covered with Pitch to hinder soaking in, was 5-13/16 inches in diameter, and weighed 2½ pounds: the Lead of 4½ pounds weight, was of a _Conical_ figure, 11. inches long, with the sharper end downwards, 1-9/16 inches at the top, and 1/16 at the bottom in diameter. And in those Experiments, made in the _Thames_, in the depth of 19. foot water, there passed between the Immersion and Emersion of the Globe, 6. seconds of an hour; and in the depth of 10. foot water, there passed 3½ seconds or thereabout: From many of which kind of Experiments it will likely not be hard to finde {149} out a method to calculate, what depth is to be concluded from any other time of the like Globes stay under water.

In the same Tryals, made with this Instrument in the said River of _Thames_, it has been found, that there is no difference in time, between the submersions of the Ball at the greatest depth, when it rose two Wherries length from the place where it was let fall (being carried by the Current of the _Tide_) and when it rose within a yard or so of the same place where it was let down.

The _other_ Instrument, for Fetching up water from the depth of the sea, is (as appears by _Figure_ 2.) a square woodden _Bucket_ C, whose bottoms _EE_, are so contrived, that as the weight A, sinks the Iron B, (to which the Bucket C, is fastned by two handles DD, on the ends of which are the moveable bottoms or Valves EE,) and thereby draws down the Bucket, the resistance of the water keeps up the Bucket in the posture C; whereby the water hath, all the while it is descending, a clear passage through; whereas, as soon as the Bucket is pulled upwards by the Line F, the resistance of the water to that motion beats the Bucket downward, and keeps it in the posture G, whereby the Included water is preserved from getting out, and the Ambient water kept from getting in.

By the advantage of which Vessel, it may be known, whether sea water be Salter at and towards the bottom, then at or near the top: Likewise, whether in some places of the sea, any sweet water is to be found at the bottom; the _Affirmative_ whereof is to be met with in the _East Indian_ Voyages of the industrious _John Hugh Van Linsckoten_, who page 16 of that Book, as 'tis _Englished_, records, that in the _Persian Gulph_, about the Island _Barem_, or _Baharem_, they fetch up with certain Vessels (which he describes not) water out of the sea, from under the salt-water, four or five fathom deep, as sweet, as any Fountain water. {150}

* * * * *

_Of the Judgement of some of the _English_ Astronomers, touching the difference between two learned men, about an Observation made of the First of the two late _Comets_._

[Sidenote: _By _Telescopical_ Stars are understood such, as are not seen, but by the help of a Telescope._]

Whereas notice has been taken in _Num._ 6. of these _Transactions_, that there was some difference between those two deservedly celebrated Philosophers, _Monsieur Hevelius_ and _Monsieur Auzout_, concerning an Observation, made by the former of them, on the 8/18 of _February_ 1665. & that thereupon some Eminent _English_ Astronomers, considering the importance of the dispute, had undertaken the examination thereof; it will, 'tis conceived, not be unacceptable to such, as saw those Papers, to be informed, what has been done and discerned by them in that matter. They having therefore compared the Printed Writings of the two Dissenters, and withall consulted the observations made with _Telescopes_ at home, by some of the most intelligent Astronomers amongst them, who have attentively observed the Position of that _Comet_ to the _Telescopical_ stars, that lay in its way; Do thereupon Joyntly conclude, that, whatever that Appearance was, which was seen near the _First Star_ of _Aries_, by _Monsieur Hevelius_ (the truth of whose relation concerning the same, they do in no wise question) the said _Comet_ did not come neer that _Star_ in the left _Ear_ of _Aries_, where the said M. _Hevelius_ supposes it to have passed, but took its course neer the _Bright Star_ in its _Left Horn_, according to _Bayers_ Tables. And since that the Observations of judicious both _French, Italian, & Dutch_ Astronomers (as many of them, as are come to the knowledge of the _English_) do in the main fully agree with theirs, they do not at all doubt, but that, there being such an unanimous {151} consent in what has been just now declared, & the Controversie being about _Matter of fact_, wherein Authority, Number, and Reputation must cast the Ballance, Mons. _Hevelius_, who is as well known for his Ingenuity, as Learning, will joyn and acquiesce in that sentiment.

* * * * *

_Of a correspondency, to be procured, for the Finding out the _True_ distance of the _Sun_ and _Moon_ from the Earth, by the _Paralax_, observed under (or neer) the same _Meridian_._

Seeing that the knowledge of this distance may prove of important Use, for the Perfecting of Astronomy, and for the better establishing the doctrine of _Refractions_, it is in the thoughts of some very curious Persons in _England_, for the finding out the same, to settle a Correspondency with some others abroad, that are understanding in Astronomical matters, and live in places farr distant in _Latitude_, and under (or near) the same _Meridian_.

To perform which, the following Method is proposed to be observed; _viz._ That at certain times agreed on by two Observatours, making use of _Telescopes_, large, good and well fitted for this purpose, by a measuring rod, placed within the Eye glass at a convenient distance, that it may be distinctly seen, and serve for measuring small distances by minuts and seconds (which is easie enough in large _Telescopes_) that, I say, each of such observers, thus furnish't shall observe the visible way of the _Moon_ among the _Fixt Stars_, (by taking her exact distance from any _Fixt Starr_, that lyes in or very near her way, together with the exact time of her so appearing) and the then apparent Diameter of her Disk; continuing these Observations every time for two or three hours; that so, {152} if possible, two exact observations of her _Apparent_ place among the _Fixt Stars_ being made, at two places thus distant in _Latitude_, and as near as may be under the same _Meridian_, by these Observators concurring at the same time, her true and exact distance may be hence collected, not onely for that time, but at all other times, by any single Observator's viewing her with a _Telescope_, and measuring exactly her _Apparent_ Diameter. It were likewise desirable, that as often as there happens any considerable _Eclipse_ of the _Sun_, that this also might be observed by them, noting therein the exact measure of the greatest Obscuration compared with the then _Apparent_ Diameter of his Disk. For by this means, after the distance of the _Moon_ hath been exactly found, the distance of the _Sun_ will easily be deduced.

As for the time, fittest for making Observations of the _Moon_, that will be, when she is about a Quarter or somewhat less illuminated, because then her light is not so bright, but that with a good _Telescope_ she may be observ'd to pass close by, and sometimes over several _Fixt Stars_; which is about four or five days before or after her Change: Or else at any other time, when the _Moon_ passes near or over some of the bigger sort of _Fixt Stars_, such as of the first or second _Magnitude_; which may be easily calculated and foreseen: Or best of all, when there is any _Totall Eclipse_ of the _Moon_; for then the smallest _Telescopical Stars_ may be seen close adjoyning to the very body of the _Moon_. Of all which particulars the two Correspondents are to agree, as soon as he, that is to joyn abroad, shall be found out; whereupon they are mutually to communicate to each other, what they shall have thus observed in each place.

* * * * *

_Of an Observation, not long since made in _England_, of _Saturn_._

This Observation was made by Mr. _William Ball_, {153} accompanied by his brother, Dr. _Ball_, _October_ 13. 1665. at six of the Clock, at _Mainhead_ near _Exeter_ in _Devonshire_, with a very good _Telescope_ near 38 foot long, and a double Eye-glass, as the observer himself takes notice, adding, that he never saw that _Planet_ more distinct. The observation is represented by _Figure_ 3. concerning which, the Author saith in his letter to a friend, as follows; This appear'd to me the present figure of _Saturn_, somewhat otherwise, than I expected, thinking it would have been decreasing, but I found it full as ever, and a little hollow above and below. Whereupon the Person, to whom notice was sent hereof, examining this shape, hath by Letters desired the worthy Author of the _Systeme of this Planet_, that he would now attentively consider the present _Figure_ of his _Anses_ or _Ring_, to see whether the appearance be to him, as in this _Figure_, and consequently whether he there meets with nothing, that may make him think, that it is not _one_ body of a Circular Figure, that embraces his _Diske_, but _two_.

And to the end that other Curious men, in other places might be engaged, to joyn their Observations with him, to see, whether they can find the like appearance to that, represented here, especially such Notches or Hollownesses, as at A and B, it was thought fit to insert here the newly related Account.

* * * * *

_A Relation of some _Mercurial_ Observations, and their Results._

Modern _Philosophers_, to avoyd Circumlocutions, call that Instrument, wherein a Cylinder of Quicksilver, of between 28. and 31. Inches in Altitude, is kept suspended after the manner of the _Torricellian_ Experiment, a _Barometer_ or _Baroscope_, first made publick by that Noble Searcher of Nature, Mr. _Boyle_, and imployed by Him and others, to detect all the minut variations in the Pressure and weight of the Air. For the more {154} curious and nice distinguishing of which small changes, Mr. _Hook_ in the _Preface_ to his _Micrography_, has described such an Instrument with a _Wheel_, contrived by himself, and, by these two last years trials of it, constantly found most exact for that purpose: which being so accurate, and not difficult to be made, it were desirable, that those who have a Genius and opportunities of making Observations of this kind, would furnish themselves with such of these Instruments, as were exactly made and adjusted according to the Method, delivered in the newly mentioned place.

To say something of the Observations, made by this Instrument, and withal to excite studious _Naturalists_ to a sedulous prosecution of the same, the _Reader_ may _first_ take notice, that the lately named Mr. _Boyle_ hath (as himself not long since did intimate to the Author of these _Tracts_) already made divers Observations of this kind in the year 1659. and 1660. before any others were publick, or by him so much as heard of; though he has hitherto forborn to divulge them, because of some other Papers (in whose Company they were to appear) which being hindred by other studies and employments, he hath not as yet finished.

_Next_, that, besides several others, who, since have had the curiosity of making such observations, the Worthy and Inquisitive Dr. _John Beal_, is doing his part with much assiduity (of which he hath by several Letters acquainted his Friends in _London_) both by observing himself, and by procuring many Correspondents in several places in _England_ for the same purpose; judging it of great importance, that Observations of this kind be made in parts somewhat distant from one another, that so from many of those, accurately made and then compared, it may be discovered, whether the Aire gravitates more in the parts of the Earth lying more _East_ or _West_, _North_ or _South_? whether on such as lie neerer to the _Sea_, or further up into the _Mainland_? in hotter or colder weather? whether in {155} high Winds or Calms? whether in wet weather or dry? whether most when a North, or when a South, when an East or a West wind blows? and whether it keeps the same seasons of Changes? and whether the seasons and changes of the Air and Weather can be thereby discover'd, and the now hidden causes of many other _Phænomena_ detected?

The said _Doctor_ is so much pleased with the discovery already made by the help of this Instrument, that he thinks it to be one of the most wonderful that ever was in the World, if we speak of strangeness, and just wonder, and of Philosophical importance, separate from the interest of lucre. For (_saith he in one of his Letters_) who could ever expect, that we men should find an Art, to weigh all the Air that hangs over our heads, in all the changes of it, and, as it were, to weigh, and to distinguish by weight, the Winds and the Clouds? Or, who did believe, that by palpable evidence we should be able to prove, the _serenest_ Air to be most heavy, and the _thickest_ Air, and when darkest Clouds hang neerest to us, ready to dissolve, or dropping, _then_ to be lightest. And though (_so he goes on_) we cannot yet reach to all the Uses and Applications of it, yet we should be entertain'd for a while, by the truly Honourable Mr. _Boyle_, as the leading person herein, upon the delight and wonder. The _Magnet_ was known many hundreds of years before it was applied to find out _New Worlds_. To me (_saith he_) tis a wonderful delight, that I have alwaies in my Study before my eye such a _Curious Ballance_.

Having thus in _General_ expressed his thoughts about this Invention, and the singular pleasure, he takes in the Observations made therewith, he descends to particulars, and in several Letters communicates them to his Correspondent, as follows:

[Sidenote: _The Exclusion of _all_ Air is here necessary, because Air being subject to the operation of Heat and Cold, if any of it remain in the _Barometer_, it will cause it to vary from shewing the true Pressure of the Air._]

1. My _Wheel-barometer_ I could never fill so exactly with _Mercury_ as to exclude _all_ Air; and therefore I trust more {156} to a _Mercurial_ Cane, and take all my Notes from it. This Cane is but 35. Inches long, of a very slender Cavity, and thick Glass. This may easily be conveyed to any place, for Trials. The Vessel for the stagnating _Mercury_, into which the said Cane is immersed, is about two _Inches_ wide. The _Mercury_ so well fill'd, that for some daies it would not subside, but hung to the top of the Glass-cane. I keep it in a Closet pretty close, 9. foot high, 8. foot broad, 15. foot long; neer a Window. This I note, because possibly the closeness of the room may hinder, that it gives not the full of all Changes, as it might in a more passable Air.

2. In all my Observations from _May_ 28. 1664 to this present (_December_ 9. 1665.) the Quicksilver never ascended but very little above 30¼ Inches.

3. It ascended very seldom so high (_videl._ to 30¼ Inches) chiefly _Decemb._ 13. 1664. the weather being fickle-fair, Evening.

4. I find by my _Calender_ of _June_ 22. 1664. at 5. in the Morning, in a time of long setled fair weather, that the _Mercury_ had ascended about half an Inch higher then 30: but I fear some mistake, because I then took no impression of _wonder_ at it; yet for 3. or 4. daies, at that time it continued high, in well-setled, fair and warm weather; most part above 30. Inches. So that I may note, the _Mercury_ to rise as high in the hottest _Summer_, as in the coldest _Winter-weather_.

[Sidenote: _Perhaps this is from some included Air._]

5. Yet surely I have noted it ascend a little higher for the Coldness of the Weather; and very frequently, both in {157} Winter and Summer to be higher in the cold Mornings and Evenings, then in the warmer Mid-day.