Micrographia Part 23

7. Whether the appearance of the _Pike_ of _Tenerif_, and several other high Mountains, at so much greater a distance then seems to agree with their respective heights, be not to be attributed to the _Curvature_ of the visual Ray, that is made by its pa.s.sing obliquely through so differingly _Dense_ a Medium from the top to the eye very far distant in the Horizon: For since we have already, I hope, made it very probable, that there is such an _inflection_ of the Rays by the differing density of the parts of the Air; and since I have found, by several Experiments made on places comparatively not very high, and have yet found the pressure sustain'd by those parts of the Air at the top and bottom, and also their differing Expansions very considerable: Insomuch that I have found the pressure of the _Atmosphere_ lighter at the top of St. _Paul_'s Steeple in _London_ (which is about two hundred foot high) then at the bottom by a sixtieth or fiftieth part, and the expansion at the top greater then that at the bottom by neer about so much also; for the _Mercurial Cylinder_ at the bottom was about 39. inches, and at the top half an inch lower; the Air also included in the Weather-gla.s.s, that at the bottom fill'd only 155. s.p.a.ces, at the top fill'd 158. though the heat at the top and bottom was found exactly the same with a scal'd _Thermometer_: I think it very rational to suppose, that the greatest Curvature of the Rays is made nearest the Earth, and that the inflection of the Rays, above 3. or 4. miles upwards, is very inconsiderable, and therefore that by this means such calculations of the height of Mountains, as are made from the distance they are visible in the Horizon, from the supposal that that Ray is a straight Line (that from the top of the Mountain is, as 'twere, a Tangent to the Horizon whence it is seen) which really is a _Curve_, is very erroneous. Whence, I suppose, proceeds the reason of the exceedingly differing Opinions and a.s.sertions of several Authors, about the height of several very high Hills.

8. Whether this Inflection of the Air will not very much alter the supposed distances of the Planets, which seem to have a very great dependence upon the Hypothetical refraction or inflection of the Air, and that refraction upon the hypothetical height and density of the Air: For since (as I hope) I have here shewn the Air to be quite otherwise then has been hitherto suppos'd, by manifesting it to be, both of a vast, at least an uncertain, height, and of an unconstant and irregular density; It must necessarily follow, that its inflection must be varied accordingly: And therefore we may hence learn, upon what sure grounds all the Astronomers. .h.i.therto have built, who have calculated the distance of the Planets from their Horizontal _Parallax_; for since the Refraction and _Parallax_ are so nearly ally'd, that the one cannot be known without the other, especially by any wayes that have been yet attempted, how uncertain must the _Parallax_ be, when the Refraction is unknown? And how easie is it for Astronomers to a.s.sign what distance they please to the Planets, and defend them, when they have such a curious _subterfuge_ as that of Refraction, wherein a very little variation will allow them liberty enough to place the Celestial Bodies at what distance they please.

If therefore we would come to any certainty in this point, we must go other wayes to work; and as I have here examined the height and refractive property of the Air by other wayes then are usual, so must we find the Parallax of the Planets by wayes not yet practiced; and to this end, I cannot imagine any better way, then the Observations of them by two persons at very far distant parts of the Earth, that lye as neer as may be under the same Meridian, or Degree of longitude, but differing as much in lat.i.tude, as there can be places conveniently found: These two persons, at certain appointed times, should (as near as could be) both at the same time, observe the way of the _Moon_, _Mars_, _Venus_, _Jupiter_, and _Saturn_, amongst the fixt Stars, with a good large _Telescope_, and making little Iconismes, or pictures, of the small fixed Stars, that appear to each of them to lye in or near the way of the Center of the Planet, and the exact measure of the apparent Diameter; from the comparing of such Observations together, we might certainly know the true distance, or Parallax, of the Planet. And having any one true Parallax of these Planets, we might very easily have the other by their apparent Diameters, which the _Telescope_ likewise affords us very accurately. And thence their motions might be much better known, and their Theories more exactly regulated. And for this purpose I know not any one place more convenient for such an Observation to be made in, then in the Island of St. _Helena_, upon the Coast of _Africk_, which lyes about sixteen degrees to the Southwards of the Line, and is very near, according to the latest Geographical Maps, in the same Meridian with _London_; for though they may not perhaps lye exactly in the same, yet their Observations, being ordered according to what I shall anon shew, it will not be difficult to find the true distance of the Planet. But were they both under the same Meridian, it would be much better.

And because Observations may be much easier, and more accurately made with good _Telescopes_, then with any other Instruments, it will not, I suppose, seem impertinent to explain a little what wayes I judge most fit and convenient for that particular. Such therefore as shall be the Observators for this purpose, should be furnished with the best _Telescopes_ that can be had, the longer the better and more exact will their Observations be, though they are somewhat the more difficultly manag'd. These should be fitted with a _Rete_, or divided Scale, plac'd at such a distance within the Eye-gla.s.s, that they may be distinctly seen, which should be the measures of minutes and seconds; by this Instrument each Observator should, at certain prefixt times, observe the Moon, or other Planet, in, or very near, the Meridian; and because it may be very difficult to find two convenient stations that will happen to be just under the same Meridian, they shall, each of them, observe the way of the Planet, both for an hour before, and an hour after, it arrive at the Meridian; and by a line, or stroke, amongst the small fixed Stars, they shall denote out the way that each of them observ'd the Center of the Planet to be mov'd in for those two hours: These Observations each of them shall repeat for many dayes together, that both it may happen, that both of them may sometimes make their Observations together, and that from divers Experiments we may be the better a.s.sured of what certainty and exactness such kind of Observations are like to prove. And because many of the Stars which may happen to come within the compa.s.s of such an _Iconism_, or Map, may be such as are only visible through a good _Telescope_, whose Positions perhaps have not been noted, nor their longitudes, or lat.i.tudes, any where remarked; therefore each Observator should indeavour to insert some fixt Star, whose longitude, and lat.i.tude, is known; or with his _Telescope_ he shall find the Position of some notable _telescopical_ Star, inserted in his Map, to some known fixt Star, whose place in the _Zodiack_ is well defin'd.

Having by this means found the true distance of the Moon, and having observed well the _apparent Diameter_ of it at that time with a good _Telescope_, it is easie enough, by one single Observation of the apparent Diameter of the Moon with a good Gla.s.s, to determine her distances in any other part of her _Orbit_, or _Dragon_, and consequently, some few Observations will tell us, whether she be mov'd in an _Ellipsis_, (which, by the way, may also be found, even now, though I think we are yet ignorant of her true distance) and next (which without such Observations, I think, we shall not be sure of) we may know exactly the bigness of that _Ellipsis_, or Circle, and her true velocity in each part, and thereby be much the better inabled to find out the true cause of all her Motions. And though, even now also, we may, by such Observations in one station, as here at _London_, observe the _apparent Diameter_ and motion of the Moon in her _Dragon_, and consequently be inabled to make a better ghess at the _Species_ or kind of Curve, in which she is mov'd, that is, whether it be sphaerical, or _elliptical_, or neither, and with what proportional velocities she is carried in that Curve; yet till her true _Parallax_ be known, we cannot determine either.

Next, for the true distance of the Sun, the best way will be, by accurate Observations, made in both these forementioned stations, of some convenient Eclipse of the Sun, many of which may so happen, as to be seen by both; for the _Penumbra_ of the Moon may, if she be sixty Semidiameters distant from the Earth, and the Sun above seven thousand, extend to about seventy degrees on the Earth, and consequently be seen by Observators as far distant as _London_, and St. _Helena_, which are not full sixty nine degrees distant. And this would much more accurately, then any way that has been yet used, determine the Parallax, and distance, of the Sun; for as for the Horizontal Parallax I have already shewn it sufficiently uncertain; nor is the way of finding it by the Eclipse of the Moon any other then hypothetical; and that by the difference of the true and apparent quadrature of the Moon is not less uncertain, witness their Deductions from it, who have made use of it; for _Vendeline_ puts that difference to be but 4'.30". whence he deduces a vast distance of the Sun, as I have before shewn. _Ricciolo_ makes it full 30'.00. but _Reinoldus_, and _Kircher_, no less then three degrees. And no wonder, for if we examine the _Theory_, we shall find it so complicated with uncertainties.

First, From the irregular surface of the Moon, and from several Parallaxes, that unless the _Dichotomy_ happen in the _Nonagesimus_ of the _Ecliptick_, and that in the Meridian, &c. all which happen so very seldom, that it is almost impossible to make them otherwise then uncertainly. Besides, we are not yet certain, but that there may be somewhat about the Moon _a.n.a.logus_ to the Air about the Earth, which may cause a refraction of the light of the Sun, and consequently make a great difference in the apparent _dichotomy_ of the Moon. Their way indeed is very rational and ingenious; and such as is much to be preferred before the way by the Horizontal Parallax, could all the uncertainties be remov'd, and were the true distance of the Moon known.

But because we find by the Experiments of _Vendiline_, _Reinoldus_, &c.

that Observations of this kind are very uncertain also: It were to be wisht, that such kind of Observations, made at two very distant stations, were promoted. And it is so much the more desirable, because, from what I have now shewn of the nature of the Air, it is evident, that the refraction may be very much greater then all the Astronomers. .h.i.therto have imagined it: And consequently, that the distance of the Moon, and other Planets, may be much lesse then what they have hitherto made it.

For first, this Inflection, I have here propounded, will allow the shadow of the Earth to be much shorter then it can be made by the other _Hypothesis_ of refraction, and consequently, the Moon will not suffer an Eclipse, unless it comes very much nearer the Earth then the Astronomers. .h.i.therto have supposed it.

Secondly, There will not in this _Hypothesis_ be any other shadow of the Earth, such as _Kepler_ supposes, and calls the _Penumbra_, which is the shadow of the refracting _Atmosphere_; for the bending of the Rays being altogether caus'd by _Inflection_, as I have already shewn, all that part which is ascribed by _Kepler_, and others after him, to the _Penumbra_, or dark part, which is without the _umbra terrae_, does clear vanish; for in this _Hypothesis_ there is no refracting surface of the Air, and consequently there can be no shadows, such as appear in the ninth Figure of the 37. _Scheme_, where let ABCD represent the Earth, and EFGH the _Atmosphere_, which according to _Keplers_ supposition, is like a Sphaere of Water terminated with an exact surface EFGH, let the lines MF, LB, ID, KH, represent the Rays of the Sun; 'tis manifest, that all the Rayes between LB, and ID, will be reflected by the surface of the Earth BAD, and consequently, the conical s.p.a.ce BOD would be dark and obscure; but, say the followers of _Kepler_, the Rays between MF, and LB, and between ID, and KH, falling on the _Atmosphere_, are refracted, both at their ingress and egress out of the _Atmosphere_, nearer towards the Axis of the sphaerical shadow CO, and consequently, inlighten a great part of that former dark Cone, and shorten, and contract, its top to N. And because of this Reflection of these Rays, say they, there is superinduc'd another sh.e.l.l of a dark Cone FPH, whose Apex P is yet further distant from the Earth: By this _Penumbra_, say they, the Moon is Eclipsed, for it alwayes pa.s.ses between the lines 12, and 34.

To which I say, That if the Air be such, as I have newly shewn it to be, and consequently cause such an inflection of the Rays that fall into it, those dark _Penumbra's_ FYZQ, HXVT, and ORPS, will all vanish. For if we suppose the Air indefinitely extended, and to be no where bounded with a determinate refracting surface, as I have shewn it uncapable of having, from the nature of it; it will follow, that the Moon will no where be totally obscured, but when it is below the Apex N, of the dark blunt Cone of the Earth's shadow: Now, from the supposition, that the Sun is distant about seven thousand Diameters, the point N, according to calculation, being not above twenty five terrestrial Semidiameters from the Center of the Earth: It follows, that whensoever the Moon eclipsed is totally darkned, without affording any kind of light, it must be within twenty five Semidiameters of the Earth, and consequently much lower then any Astronomers have hitherto put it.

This will seem much more consonant to the rest of the secundary Planets; for the highest of _Jupiter's_ Moons is between twenty and thirty _Jovial Semidiameters_ distant from the Center of _Jupiter_; and the Moons of _Saturn_ much about the same number of _Saturnial Semidiameters_ from the Center of that Planet.

But these are but conjectures also, and must be determin'd by such kind of Observations as I have newly mention'd.

Nor will it be difficult, by this _Hypothesis_, to salve all the appearances of Eclipses of the Moon, for in this _Hypothesis_ also, there will be on each side of the shadow of the Earth, a _Penumbra_, not caus'd by the Refraction of the Air, as in the _Hypothesis_ of _Kepler_; but by the faint inlightning of it by the Sun: For if, in the sixth Figure, we suppose ESQ, and GSR, to be the Rays that terminate the shadow from either side of the Earth; ESQ coming from the upper limb of the Sun, and GSR from the under; it will follow, that the shadow of the Earth, within those Rays, that is, the Cone GSE, will be totally dark. But the Sun being not a point, but a large _area_ of light, there will be a secondary dark Cone of shadow EPG, which will be caus'd by the earth's hindring part of the Rays of the Sun from falling on the parts GPR, and EPQ, of which halved shadow, or _Penumbra_, that part will appear brightest which lyes nearest the terminating Rayes GP, and EP, and those darker that lye nearest to GS, and ES: when therefore the Moon appears quite dark in the middle of the Eclipse, she must be below S, that is, between S and F; when she appears lighter near the middle of the Eclipse, she must pa.s.s some where between RQ and S; and when she is alike light through the whole Eclypse, she must pa.s.s between RQ, and P.

Observ. LIX. _Of mult.i.tudes of small _Stars_ discoverable by the _Telescope_._

Having, in the last Observation, premis'd some particulars observable in the _medium_, through which we must look upon _Coelestial_ Objects, I shall here add one Observation of the Bodies themselves; and for a _specimen_ I have made choice of the _Pleiades_, or seven Stars, commonly so called (though in our time and Climate there appear no more then six to the naked eye) and this I did the rather, because the deservedly famous _Galileo_, having publisht a Picture of this _Asterisme_, was able, it seems, with his Gla.s.s to discover no more then thirty six, whereas with a pretty good twelve foot _Telescope_, by which I drew this 38 _Iconism_, I could very plainly discover seventy eight, placed in the order they are ranged in the Figure, and of as many differing Magnitudes as the _Asterisks_, wherewith they are Marked, do specifie; there being no less then fourteen several Magnitudes of those Stars, which are compris'd within the draught, the biggest whereof is not accounted greater then one of the third Magnitude; and indeed that account is much too big, if it be compared with other Stars of the third Magnitude, especially by the help of a _Telescope_; for then by it may be perceiv'd, that its splendor, to the naked eye, may be somewhat augmented by the three little Stars immediately above it, which are near adjoyning to it. The _Telescope_ also discovers a great variety, even in the bigness of those, commonly reckon'd, of the first, second, third, fourth, fifth, and sixth Magnitude; so that should they be distinguish'd thereby, those six Magnitudes would, at least, afford no less then thrice that number of Magnitudes, plainly enough distinguishable by their Magnitude, and brightness; so that a good twelve foot Gla.s.s would afford us no less then twenty five several Magnitudes. Nor are these all, but a longer Gla.s.s does yet further, both more nicely distinguish the Magnitudes of those already noted, and also discover several other of smaller Magnitudes, not discernable by the twelve foot Gla.s.s: Thus have I been able, with a good thirty six foot Gla.s.s, to discover many more Stars in the _Pleiades_ then are here delineated, and those of three or four distinct Magnitudes less then any of those spots of the fourteenth Magnitude. And by the twinkling of divers other places of this _Asterisme_, when the Sky was very clear, I am apt to think, that with longer Gla.s.ses, or such as would bear a bigger _aperture_, there might be discovered mult.i.tudes of other small Stars, yet inconspicuous. And indeed, for the discovery of small Stars, the bigger the _aperture_ be, the better adapted is the Gla.s.s; for though perhaps it does make the several specks more radiant, and glaring, yet by that means, uniting more Rays very near to one point, it does make many of those radiant points conspicuous, which, by putting on a less _aperture_, may be found to vanish; and therefore, both for the discovery of the fixt Star, and for finding the _Satellites_ of _Jupiter_, before it be out of the day, or twilight, I alwayes leave the Object-gla.s.s as clear without any _aperture_ as I can, and have thereby been able to discover the _Satellites_ a long while before; I was able to discern them, when the smaller _apertures_ were put on; and at other times, to see mult.i.tudes of other smaller Stars, which a smaller _aperture_ makes to disappear.

In that notable _Asterism_ also of the Sword of _Orion_, where the ingenious Monsieur _Hugens van Zulichem_ has discovered only three little Stars in a cl.u.s.ter, I have with a thirty six foot Gla.s.s, without any _aperture_ (the breadth of the Gla.s.s being about some three inches and a half) discover'd five, and the twinkling of divers others up and down in divers parts of that small milky Cloud.

So that 'tis not unlikely, but that the meliorating of _Telescopes_ will afford as great a variety of new Discoveries in the Heavens, as better _Microscopes_ would among small terrestrial Bodies, and both would give us infinite cause, more and more to admire the omnipotence of the Creator.

Observ. LX. _Of the _Moon_._

Having a pretty large corner of the Plate for the seven Starrs, void, for the filling it up, I have added one small _Specimen_ of the appearance of the parts of the Moon, by describing a small spot of it, which, though taken notice of, both by the Excellent _Hevelius_, and called _Mons Olympus_ (though I think somewhat improperly, being rather a vale) and represented by the Figure X. of the 38. _Scheme_, and also by the Learn'd _Ricciolus_, who calls it _Hipparchus_, and describes it by the Figure Y, yet how far short both of them come of the truth, may be somewhat perceiv'd by the draught, which I have here added of it, in the Figure Z, (which I drew by a thirty foot Gla.s.s, in _October_ 1664. just before the Moon was half inlightned) but much better by the Reader's diligently observing it himself, at a convenient time, with a Gla.s.s of that length, and much better yet with one of threescore foot long, for through these it appears a very s.p.a.cious Vale, incompa.s.sed with a ridge of Hills, not very high in comparison of many other in the Moon, nor yet very steep. The Vale it self ABCD, is much of the figure of a Pear, and from several appearances of it, seems to be some very fruitful place, that is, to have its surface all covered over with some kinds of vegetable substances; for in all positions of the light on it, it seems to give a much fainter reflection then the more barren tops of the incompa.s.sing Hills, and those a much fainter then divers other cragged, chalky, or rocky Mountains of the Moon. So that I am not unapt to think, that the Vale may have Vegetables _a.n.a.logus_ to our Gra.s.s, Shrubs, and Trees; and most of these incompa.s.sing Hills may be covered with so thin a vegetable Coat, as we may observe the Hills with us to be, such as the short Sheep pasture which covers the Hills of _Salisbury_ Plains.

Up and down in several parts of this place here describ'd (as there are mult.i.tudes in other places all over the surface of the Moon) may be perceived several kinds of pits, which are shap'd almost like a dish, some bigger, some less, some shallower, some deeper, that is, they seem to be a hollow _Hemisphere_, incompa.s.sed with a round rising bank, as if the substance in the middle had been digg'd up, and thrown on either side.

These seem to me to have been the effects of some motions within the body of the Moon, _a.n.a.logus_ to our Earthquakes, by the eruption of which, as it has thrown up a brim, or ridge, round about, higher then the Ambient surface of the Moon, so has it left a hole, or depression, in the middle, proportionably lower; divers places resembling some of these, I have observ'd here in _England_, on the tops of some Hills, which might have been caus'd by some Earthquake in the younger dayes of the world. But that which does most incline me to this belief, is, first, the generality and diversity of the Magnitude of these pits all over the body of the Moon.

Next, the two experimental wayes, by which I have made a representation of them.

The first was with a very soft and well temper'd mixture of Tobacco-pipe clay and Water, into which, if I let fall any heavy body, as a Bullet, it would throw up the mixture round the place, which for a while would make a representation, not unlike these of the Moon; but considering the state and condition of the Moon, there seems not any probability to imagine, that it should proceed from any cause _a.n.a.logus_ to this; for it would be difficult to imagine whence those bodies should come; and next, how the substance of the Moon should be so soft; but if a Bubble be blown under the surface of it, and suffer'd to rise, and break; or if a Bullet, or other body, sunk in it, be pull'd out from it, these departing bodies leave an impression on the surface of the mixture, exactly like these of the Moon, save that these also quickly subside and vanish. But the second, and most notable, representation was, what I observ'd in a pot of boyling Alabaster, for there that powder being by the eruption of vapours reduc'd to a kind of fluid consistence, if, whil'st it boyls, it be gently remov'd besides the fire, the Alabaster presently ceasing to boyl, the whole surface, especially that where some of the last Bubbles have risen, will appear all over covered with small pits, exactly shap'd like these of the Moon, and by holding a lighted Candle in a large dark Room, in divers positions to this surface, you may exactly represent all the _Phaenomena_ of these pits in the Moon, according as they are more or less inlightned by the Sun.

And that there may have been in the Moon some such motion as this, which may have made these pits, will seem the more probable, if we suppose it like our Earth, for the Earthquakes here with us seem to proceed from some such cause, as the boyling of the pot of Alabaster, there seeming to be generated in the Earth from some subterraneous fires, or heat, great quant.i.ties of vapours, that is, of expanded aerial substances, which not presently finding a pa.s.sage through the ambient parts of the Earth, do, as they are increased by the supplying and generating principles, and thereby (having not sufficient room to expand themselves) extreamly condens'd, at last overpower, with their _elastick_ properties, the resistence of the incompa.s.sing Earth, and lifting it up, or cleaving it, and so shattering of the parts of the Earth above it, do at length, where they find the parts of the Earth above them more loose, make their way upwards, and carrying a great part of the Earth before them, not only raise a small brim round about the place, out of which they break, but for the most part considerable high Hills and Mountains, and when they break from under the Sea, divers times, mountainous Islands; this seems confirm'd by the _Vulcans_ in several places of the Earth, the mouths of which, for the most part, are incompa.s.sed with a Hill of a considerable height, and the tops of those Hills, or Mountains, are usually shap'd very much like these pits, or dishes, of the Moon: Instances of this we have in the descriptions of _aetna_ in _Sicily_, of _Hecla_ in _Iceland_, of _Tenerif_ in the _Canaries_, of the several _Vulcans_ in _New-Spain_, describ'd by _Gage_, and more especially in the eruption of late years in one of the _Canary_ Islands. In all of which there is not only a considerable high Hill raised about the mouth of the _Vulcan_, but, like the spots of the Moon, the top of those Hills are like a dish, or bason. And indeed, if one attentively consider the nature of the thing, one may find sufficient reason to judge, that it cannot be otherwise; for these eruptions, whether of fire, or smoak, alwayes raysing great quant.i.ties of Earth before them, must necessarily, by the fall of those parts on either side, raise very considerable heaps.

Now, both from the figures of them, and from several other circ.u.mstances; these pits in the Moon seem to have been generated much after the same manner that the holes in Alabaster, and the _Vulcans_ of the Earth are made. For first, it is not improbable, but that the substance of the Moon may be very much like that of our Earth, that is, may consist of an earthy, sandy, or rocky substance, in several of its superficial parts, which parts being agitated, undermin'd, or heav'd up, by eruptions of vapours, may naturally be thrown into the same kind of figured holes, as the small dust, or powder of Alabaster. Next, it is not improbable, but that there may be generated, within the body of the Moon, divers such kind of internal fires and heats, as may produce such Exhalations; for since we can plainly enough discover with a _Telescope_, that there are mult.i.tudes of such kind of eruptions in the body of the Sun it self, which is accounted the most n.o.ble aetherial body, certainly we need not be much scandaliz'd at such kind of alterations, or corruptions, in the body of this lower and less considerable part of the universe, the Moon, which is only secundary, or attendant, on the bigger, and more considerable body of the Earth. Thirdly, 'tis not unlikely, but that supposing such a sandy or mouldring substance to be there found, and supposing also a possibility of the generation of the internal _elastical_ body (whether you will call it air or vapours) 'tis not unlikely, I say, but that there is in the Moon a principle of gravitation, such as in the Earth. And to make this probable, I think, we need no better Argument, then the roundness, or globular Figure of the body of the Moon it self, which we may perceive very plainly by the _Telescope_, to be (bating the small inequality of the Hills and Vales in it, which are all of them likewise shap'd, or levelled, as it were, to answer to the center of the Moons body) perfectly of a Sphaerical figure, that is, all the parts of it are so rang'd (bating the comparitively small ruggedness of the Hills and Dales) that the outmost bounds of them are equally distant from the Center of the Moon, and consequently, it is exceedingly probable also, that they are equidistant from the Center of gravitation; and indeed, the figure of the superficial parts of the Moon are so exactly shap'd, according as they should be, supposing it had a gravitating principle as the Earth has, that even the figure of those parts themselves is of sufficient efficacy to make the gravitation, and the other two suppositions probable: so that the other suppositions may be rather prov'd by this considerable Circ.u.mstance, or Observation, then this suppos'd Explication can by them; for he that shall attentively observe with an excellent _Telescope_, how all the Circ.u.mstances, notable in the shape of the superficial parts, are, as it were, exactly adapted to suit with such a principle, will, if he well considers the usual method of Nature in its other proceedings, find abundant argument to believe it to have really there also such a principle; for I could never observe, among all the mountainous or prominent parts of the Moon (whereof there is a huge variety) that any one part of it was plac'd in such a manner, that if there should be a gravitating, or attracting principle in the body of the Moon, it would make that part to fall, or be mov'd out of its visible posture.

Next, the shape and position of the parts is such, that they all seem put into those very shapes they are in by a gravitating power: For first, there are but very few clifts, or very steep declivities in the ascent of these Mountains; for besides those Mountains, which are by _Hevelius_ call'd the _Apennine_ Mountains, and some other, which seem to border on the Seas of the Moon, and those only upon one side, as is common also in those Hills that are here on the Earth; there are very few that seem to have very steep ascents, but, for the most part, they are made very round, and much resemble the make of the Hills and Mountains also of the Earth; this may be partly perceived by the Hills incompa.s.sing this Vale, which I have here describ'd; and as on the Earth also, the middlemost of these Hills seems the highest, so is it obvious also, through a good _Telescope_, in those of the Moon; the Vales also in many are much shap'd like those of the Earth, and I am apt to think, that could we look upon the Earth from the Moon, with a good _Telescope_, we might easily enough perceive its surface to be very much like that of the Moon.

Now whereas in this small draught, (as there would be mult.i.tudes if the whole Moon were drawn after this manner) there are several little Ebullitions, or Dishes, even in the Vales themselves, and in the incompa.s.sing Hills also; this will, from this supposition, (which I have, I think, upon very good reason taken) be exceeding easily explicable; for, as I have several times also observ'd, in the surface of Alabaster so ordered, as I before describ'd, so may the later eruptions of vapours be even in the middle, or on the edges of the former; and other succeeding these also in time may be in the middle or edges of these, &c. of which there are Instances enough in divers parts of the body of the Moon, and by a boyling pot of Alabaster will be sufficiently exemplifi'd.

To conclude therefore, it being very probable, that the Moon has a principle of gravitation, it affords an excellent distinguishing Instance in the search after the cause of gravitation, or attraction, to hint, that it does not depend upon the diurnal or turbinated motion of the Earth, as some have somewhat inconsiderately supposed and affirmed it to do; for if the Moon has an attractive principle, whereby it is not only shap'd round, but does firmly contain and hold all its parts united, though many of them seem as loose as the sand on the Earth, and that the Moon is not mov'd about its Center; then certainly the turbination cannot be the cause of the attraction of the Earth, and therefore some other principle must be thought of, that will agree with all the secundary as well as primary Planets. But this, I confess, is but a probability, and not a demonstration, which (from any Observation yet made) it seems hardly capable of, though how successful future indeavours (promoted by the meliorating of Gla.s.ses, and observing particular circ.u.mstances) may be in this, or any other, kind, must be with patience expected.

_FINIS._

THE TABLE.

Observat. 1. Of the point of a Needle.

_A Description of it: what other Bodies have the sharpest points: of the ruggedness of polisht Metal. A description of a printed point. Of very small writing, and the use of it for secret intelligence: the cause of the coursness of printed lines and points._

Observ. 2. Of the Edge of a Razor.

_A description of it: the causes of its roughness: of the roughness of very well polisht Optick Gla.s.ses._.

Obser. 3. Of fine Lawn.

_A description of it: A silken Flax mention'd, an attempt to explicate the _Phaenomena_ of it, with a conjecture at the cause of the gloss of Silk._

Observ. 4. Of Tabby.

_A short description of it. A conjecture about the reason why Silk is so susceptible of vivid colours: and why Flax and Hair is not. A conjecture, that it way perhaps be possible to spin a kind of artificial Silk, out of some glutinous substance that may equalize natural Silk._

Observ. 5. Of water'd Silks.

_The great unaccurateness of artificial works. A description of a piece of water'd Silk; an Explication of the cause of the _Phaenomena_: the way by which that operation is perform'd: some other _Phaenomena_ mention'd depending on the same cause._

Observ. 6. Of Gla.s.s-Canes.

_The exceeding smallness of some of these Bodies. By what means the hollowness of these small pipes was discover'd: several _Phaenomena_ of it mention'd. An attempt to explicate them from the congruity and incongruity of Bodies: what those proprieties are. A hypothetical explication of fluidity: of the fluidity of the air, and several other _Phaenomena_ of it: of congruity & incongruity; ill.u.s.trated with several Experiments: what effects may be ascrib'd to these properties: an explication of the roundness of the surface of fluid Bodies: how the ingress of fluid bodies into a small hole of an heterogenious body is hindred by incongruity; a mult.i.tude of _Phaenomena_ explicable hereby. Several Quaeries propounded; 1.

Concerning the propagation of light through differing mediums. 2.

Concerning Gravity. 3. Concerning the roundness of the Sun, Moon, and Planets. 4. Concerning the roundness of Fruits, Stones, and divers artificial Bodies. His Highness Prince _Rupert's_ way of making Shot. Of the roundness of Hail. Of the grain of _Kettering_ Stone, and of the Sparks of fire. 5. Concerning springiness and tenacity. 6. Concerning the original of Fountains; several Histories and Experiments relating thereto. 7.

Concerning the dissolution of Bodies in Liquors. 8. Concerning the universality of this Principle: what method was taken in making and applying experiments. The explication of filtration, and several other _Phaenomena_; such as the motion of Bodies on the surface of Liquors; several Experiments mention'd to this purpose. Of the height to which the water may rise in these Pipes; and a conjecture about the juices of Vegetables, & the use of their pores. A further explication of Congruity: And an attempt of solving the _Phaenomena_ of the strange Experiment of the suspension of the _Mercury_ at a much greater height then thirty inches.

The efficacy of immediate contact, and the reason of it._