And calculate the Stars, how they will weild
The mighty Frame! how build, unbuild, contrive
To save Appearances, how gird the Sphere
With centric and eccentric scribbl'd o'er;
Cycle, and Epicycle, Orb in Orb.
But the following Synopsis, I believe, will abundantly convince you
that from certain Observations only, we ought to form all our Notions
of it, if we either hope to arrive at Truth, or expect our Ideas should
be supported by Reason.
Aristotle was of Opinion, that the Universe, or Heaven, was all one
World, and St. Chrysostom, Tertullian, St. Bonaventure, Tycho Brahe,
Longomontanus, Kepler, Bulialdus and Tellez, were of an united Opinion,
that this one Heaven, or Universe, was all sidereal and fluid. But
Aegidius, Hurtadus, Cisalpinus, and Aversa, believing the same Heaven
with them to be all one World, and that sidereal, yet on the contrary
held it to be solid.
Clemens, Acacius, Theodoret, Anastasius, Synaita, Procopius, Suidus, S.
Bruno, and Claudianus Mamertus, supposed the universal mundane Space as
divided into two Heavens, namely,
The Empyræum created the first Day,
And the Firmament created the second Day.
Two Heavens were also held by Justin Martyr, the one sidereal, and the
other aerial. The first supposed by St. Gregory Nyssene, to be that of
the fixed Stars, and the last, that of the Planets. But _Mastrius_ and
_Bellutus_, though agreeing in the Number of Heavens, calls one the
_*Primum Mobile_, and the other, the Starry Heaven.
Farther, St. Basil, St. Ambrose, Damascene, Cassiodorus, Genebrardus,
Suarez, Tannerus, Hurtadus, Oviedus, Tellez, and Borrus, distinguished
the Universe as divided into three Portions, or Heavens.
Or, as _Cajetan_. _Tho. Aquinas._
The first called the Empyræum, Watery,
The second supposed Sidereal, Sidereal, Watery,
And the last of all, Aerial. Aerial, Sidereal.
Again, St. _Athanasius_ adds to those of the fix'd Stars, the Planets,
and the Air, that of the _Empyræum_, and makes in all four Heavens.
But as the Number of the Heavens thus increases, and will become
subdivided in the subsequent Account of them, to give you a better Idea
of the Order of these celestial Portions of the mundane Space, it will
not be amiss to form what remains of them into regular Sections of
their proper Spheres and Systems.
See _Plate_ III. in which Figure, the first represents a Section of the
cosmical Theory of _Oviedus_ and _Ricciolus_: Both consisting of five
Heavens, _viz._
By _Oviedus_, By _Ricciolus_,
sidereal and solid. sidereal and fluid.
The fixed Stars, A _Empyræum_, G
_Saturn_, B The Water, F
_Jupiter_, C The fixed Stars, A
_Sol_, with ♂ ☿ and ♀ included, D The Planets, H
The Moon. E The Air. I
_Fig._ II. represents that of venerable _Bede_ and _Rabanus_, _viz._ of
Seven Heavens.
And according to _Bede_ But by _Rabanus_,
composed of
The Air, P The Atmosphere,
The Æther, O The upper Air,
_Olympus_, N The inferior Fire,
The Element of Fire, M The superior Fire,
The Firmament, A Sphere of the fixed Stars,
The Angelical Region, L The Crystalline Heaven,
Realm of the Trinity. K The _Empyræum_.
Fig. III. Represents the Hypotheses of _Eudoxus_, _Plato_, _Calippus_,
_Cicero_, _Riccius_, _Philo_, _Remigius_, _Aben-Ezra_, _Carthusianus_,
_Lyranus_, _Tostatus_, _Brugensis_, _Orontius_, _Cremoninus_,
_Philalethæus_, _Amicus_, and _Ruvius_; also the _Babylonians_ and
_Egyptians_.
Consisting of Eight Heavens,
All Sidereal, _viz._ The Sphere of the fix'd Stars, and those of the
Seven Planets.
Fig. IV. is that of _Macrobius_, _Haly Alpetragius_, _Rabbi-Josue_,
_Rabbi Moyses_, _Scotus_, _Abraham Zagutus_, _Sacroboscus_,
_Claromontius_, _Avigra_, and _Arraiga_.
All of Nine Heavens,
Comprehend a _Primum Mobile_ Q, or, according to _Arriaga_, a solid
_Empyræum_. The Sphere, of fixed Stars A, and the seven Regions of the
solar Planets.
Fig. V. is that of the great _Alphonsus_, _Fernelius_, _Regiomontanus_,
_Amicus_, _Maurolycus_ and _Langius_; also of _Azabel_, _Thebit_,
and _Isaac Israelita_; and likewise of _Gulielmus Parisiensis_, and
_Johannes Antonius Delphinus_.
Consisting of Ten Heavens, made up of
A _Primum Mobile_ S _Empyræum_.
A Sphere of _Tripidation_ in Longitude R _Primum Mobile_.
The Sphere of the fixed Stars A
And those of the seven solar Planets within.
_Note_, Some Authors place the Sphere of _Tripidation_ in Longitude
below that of the _Aplain_, or Eighth Sphere.
Lastly, Fig. VI. is the Heaven of _Petrus Alliacensis_, the College
of _Conimbra_, _Martinensis_, (and sometime) of _Clavius_; and also
_Johannes Warnerus_, _Leopoldus de Austriâ_, _Johannes Antonius
Maginus_; and lastly, of _Clavius_.
In all Eleven Heavens containing,
T A _Primum Mobile_, or, as others say, an _Empyræum_.
V A Sphere of Libration in Latitude.
W A Sphere of Libration in Longitude.
A The Sphere of the fixed Stars, and those of the Planets.
[Illustration: Plate III.
The Seven Planetary orbits.
]
Thus you see how many various Opinions have from time to time been
embraced concerning the Fabric and Formation of the visible Universe;
all of which are now and have long been exploded; and although at
first advanced by Men of the greatest Learning, and of the deepest
Penetration in natural Knowledge, it does not appear from any one of
their Opinions, that they had any the least Notion of infinite Space,
but as it were confined the Divine Being to their limited Notions,
as one may say in an Egg-shell. If therefore what I shall hereafter
advance, extend so far without the known Creation, that you can
possibly conceive no Bounds to the Works of infinite Wisdom and Power,
I hope you will be in no Danger of looking upon it as more ridiculous,
or absurd, than what so many of the wisest Men of every Age have
thought proper to attempt, and have judged worthy of their Attention
so long before me. If any thing less so, I shall think myself happy
enough in having broke, or rather passed the narrow Limits to which the
Creation has for so many Years been confined, in hopes of tempting Men
of greater Talents to look up wards, and pursue so noble a Subject as
far as the human Understanding is capable of comprehending it.
To the Opinions above might be added many more, particularly that of
_Johannes Baptista Turrianus_, and _Fracastorius_, who increased the
Number of Heavens to fourteen, _viz._ seven on each Side the _Aplané_.
But of this I have said enough; in my next I shall proceed to Matter
better grounded,
_And am_, &c.
[Illustration]
LETTER the THIRD.
_Concerning the Nature, Magnitude, and Motion of the Planetary Bodies
round the Sun_, &c.
_SIR_,
The younger _Pliny_, if I remember right, somewhere says, that there
is, or ought to be, a wide Difference betwixt writing to a Friend, and
writing to the Publick: I have indeed pleased myself with the one, but
am far from thinking myself qualified for the other; I must therefore
rather intreat you, though perhaps you cannot possibly overlook all
my Faults as an Author, to excuse them at least in the Friend, and by
such kind of unlimited Indulgence, you will give me a much greater
Chance to do the Subject some Justice, though I own I despair in this
first Attempt, to reconcile every thing I advance to your more cool and
impartial Reasoning. But to the Business:
As I have no Ambition to have the Substance of my Theory more admired
by you than understood, which is too often the Case in Works of
this Nature, I must beg leave to repeat to you Part of a former
Discourse, which will refresh in your Ideas the principal Laws of the
System of our Sun, and make you properly acquainted with such Things
as are necessary to be known in the now-established Astronomy of
[I]_Copernicus_, &c. before I proceed to any new Matter.
[Footnote I: Nicolaus Copernicus, stiled by _Bulialdus_, _Vir absolutæ
subtilitatis_, was a Native of _Thorn_ in _Polish Prussia_, and Canon
of the Church of _Frawenburgh_; he was Scholar to _Dominicus Maria_ of
_Ferrara_, to whom he was Assistant in his astronomical Observations
at _Bologne_, and Professor of the Mathematicks at _Rome_, in his
noble Work, _De Revolutionibus Orbium Cælestium_; he fortunately
revived, happily united, and formed into an Hypothesis of his own, the
several Opinions of _Philolaus_, _Heraclides Ponticus_, and _Ecphantus
Pythagoreus_, _viz._ after the Opinion of _Philolaus_ he made the
Earth to move about the Sun, as the Center of its annual Motion; and
according to _Heraclides_ and _Ecphantus_, he likewise gave it a
diurnal Rotation round its own Axis: Which System has withstood all
Opposition; and as _Ricciolus_, (though a Dissenter from it) observes,
_Per damna, per cædes, ab ipso sumit opes, animumque ferro._]
The Sun, you are not to learn, is the reputed Center of our _Planetary
System_, and may remember, that the Earth on which we live, and these
five following _Erratic Stars_, viz. Saturn, Jupiter, Mars, Venus and
Mercury, have been demonstrated to move round him in the Order and
Manner following.
_Saturn_ is found to complete one Revolution round the Sun in
twenty-nine Years, one hundred and seventy-four Days, six Hours,
and thirty-six Minutes; at the Distance of about seven hundred and
seventy-seven Millions of Miles. _Jupiter_ performs a like Revolution
in about eleven Years, three hundred and seventeen Days, twelve
Hours, and twenty Minutes; distant from the Sun about four hundred
and twenty-four Millions of Miles. _Mars_ compleats his Circuit in
one Year, three hundred and twenty-one Days, twenty-three Hours, and
twenty-seven Minutes; and his mean Distance is about one hundred and
twenty-three Millions of Miles.
These three are called superior Planets, as being farther from the Sun
than the Earth, and circumscribing its Orbit.
The Earth circumambulates her Orbit in one solar Year, _viz._ in three
hundred and sixty-five Days, five Hours, forty-eight Minutes, and
fifty-seven Seconds; at the mean Distance of eighty-one Millions of
Miles.
The Radius of _Venus's_ Orbit is about fifty-nine Millions of Miles;
and that of _Mercury_ nearly thirty-two Millions, _ditto_.
The Heliocentric Revolution of _Venus_, is made in two hundred and
twenty-four Days, sixteen Hours, forty-nine Minutes, and twenty-seven
Seconds; and that of _Mercury_, in eighty-seven Days, twenty-three
Hours, fifteen Minutes, and fifty-four Seconds. These two last Planets
are called inferior Ones, as being circumscribed by the Earth.
The Diameter of the Sun being demonstrated to be nearly seven hundred
and sixty-three thousand Miles:
The proportional Magnitudes of all the above Planets will be found
nearly as follows, _viz._
The Diameter of the Globe,
Of _Mercury_ 4,240 }
_Venus_ 7,900 }
the Earth 7,970 } Miles.
_Mars_ 4,440 }
_Jupiter_ 81,000 }
and _Saturn_ 61,000 }
Thus much I have thought proper to premise, and for your immediate
Inspection, have added the following Schemes, that nothing may be
wanting to give a general Idea of the Order of the celestial Bodies in
our own System, before I attempt to lead you through the neighbouring
Regions of the Stars to the more remote Tracts of Infinity.
PLATE IV.
Is a true Delineation of the solar System, with the Trajectories of
three of the principal Comets, whose Periods and Orbits have been
accurately determined, and are represented in their true Proportion and
Position to one another, and the Order of the Planets round the Sun,
marked with their respective Characters, _viz._ ♄, for _Saturn_, ♃,
_Jupiter_, ♂, _Mars_, ♁, the Earth, ♀, _Venus_, and ☿, _Mercury_. The
Scale being nearly five hundred and eighteen Millions of Miles to an
Inch.
PLATE V.
Is a true Projection of the System of the known Comets; in which are
represented nine of the chief Trajectories, from their _Aphelii_ to
their _Perihelii_, all in just Proportion and Position to the Orbits
of _Saturn_ and _Jupiter_, which are also represented by the two
concentric Circles, supposed to be drawn round the Sun as their Center.
The Ellipsis, or Trajectory, marked A, shews the Position and Path of
the Comet which appeared in the Year 1684, whose Period is supposed to
be about fifty Years, and has been observed within the Region of the
Planets once.
That mark'd B, is the Way of the Comet of 1682;
The Period conjectured to be about seventy-five
Years and a half, and has been observed thrice.
C, Way of the Comet of 1337;
The Period about 100 Years, observed once.
D, That of the Comet of 1661;
The Period about 129 Years, observed twice.
E, Tract of the Comet of 1618;
The Period about 160 Years, observed once.
F, Way of the Comet of 1677;
The Period about 200 Years, observed once.
G, Way of the Comet of 1744;
The Period about 300 Years, observed once.
H, Way of the Comet of 1665;
The Period about 400 Years, observed once.
I, Way of the Comet of 1680;
The Period about 575 Years, observed thrice.
[Illustration: Plate IV.]
[Illustration: Plate V.]
The Scale of this System is equal to one Third of the former.
Here I must observe to you, as a Thing I judge may prove of great
Consequence with regard to the System of Comets, which is as yet very
imperfect: That I am strongly of Opinion, that the Comets in general,
through all their respective Orbits, describe one common Area, that is
to say, all their Orbits with regard to the Magnitude of their proper
Planes, are mathematically equal to one another; which, if it once
could be proved, and confirmed by Observation, the Theories of all the
Comets that have been justly observed, might easily be perfected, and
their Periods at once determined, which now we can only guess at, or
may wait whole Ages for more Certainty of. What leads me to believe,
that this may prove to be really the Case is this.
I find by Calculation, that the Orbits of the two last Comets, whose
Elements have been most corrected by Sir _Isaac Newton_ and Dr.
_Hally_, are to one another, according to their Numbers, nearly as
[J]13 to [K]17, notwithstanding one of them is one of the most erratick
that ever came under our Observation; and the other one of the most
neighbouring to the Sun.
[Footnote J: 1316539,968282 Comet of 1680.]
[Footnote K: 1708155,4644 Comet of 1682.]
But it is well known to all Mathematicians, that the first of these
Comets moved in so eccentric a Trajectory, that the least Error in its
almost incredible Proximity to the Sun will produce a very sensible
Difference in the Area of the Orbit: And accordingly, if we moderate
the Perihelion Distance of this Comet, by making it but 1000 instead of
[L]612, which is but increasing it a 1/35000th Part of the great Radius
of the Orbit, (which is an Error every Astronomer will readily grant is
very easily made) and we shall find the Orbits of the said two Comets
to be exactly equal.
[Footnote L: The Number in Dr. _Hally's_ Synopsis.]
Further, I must inform you, that the Comet of 1682, which the above is
compared with, seems to have been so accurately observed, that it does
not appear to have altered its Perihelion Distance half a 68th Part in
one intire Revolution. Now, if we can with any Show of Reason, and a
Probability on our Side, bring the Areas of these two extream Comets,
as I may call them, to an _Equality_, sure we may conclude, it is a
Subject highly worthy to be more considered and enquired into.
PLATE VI.
Is a true Representation of the satellite Systems, proportionable to
one another, and to the Orb of the Sun's Body, that a just Idea of the
Distances of those secondary Planets, may be easier had from their
respective primary ones.
S represents the solar Body with its Atmosphere. _Fig._ 1. is the
System of _Saturn_ from the same Scale. _Fig._ 2. that of _Jupiter_
from _ditto_. And _Fig._ 3. the Orbit of the Moon round the Earth, in
the same Proportion.
But as you can have but a very imperfect Idea of the Magnitude of these
last Circles, with regard to the Body of the Earth or Moon,
PLATE VII.
Is a true Projection of their real Globes, at their proper Distance
from each other, with their common Center of Gravity, and the Point and
Line of equal Suspension betwixt them, _viz._
A, represents the Globe of the Earth.
B, that of the Moon.
C, Point, and C D, Line of equal Suspension betwixt them.
E, Common Center of Gravity, which describes the _Orbis Magnus_.
E, F, and B, G, is the Orbit of the Moon.
Farther, that nothing may be wanting to give a true Notion of the whole
together,
PLATE VIII.
Is a proportional Drawing of all the primary and secondary Planets
together, distinguished by their Characters, proper to attend a Globe
of twelve Inches Diameter, such a one being supposed to represent the
Sun.
PLATE IX.
Is an exact Scheme of the principal known Comets, in just Proportion,
to the Globe of the Earth represented at A, with the Nucleus, and Part
of the Tail of the Comet of 1680, B, as it was observed in its Assent
from the Sun, _viz._ _a a_ the Comet's natural Atmosphere, _z z z_, the
_Denser Matter_ winding itself into the Axis of the Train _x x_, the
inflam'd Atmosphere and Tail dilated near the Sun. C, represents the
Ball of the Comet of 1682, D, that of 1665, E, that of 1742, and F, the
Head of the Comet of 1744.
And again, that you may have some Notion of the apparent Magnitudes of
all these Planets and Comets, _&c._ as they appear at the Earth,
[Illustration: Plate VI.]
[Illustration: Plate VII.]
[Illustration: Plate VIII.]
[Illustration: Plate IX.]
[Illustration: Plate X.]
[Illustration: Plate XI.]
PLATE X.
Represents the Sun and Moon in the just Proportion of their mean
Diameters, with two of the Comets A and B, and the five erratick
Planets, as they are observed at the Earth, in a middle State of their
Distances from it.
For a more full and particular Description of all the Parts of the
solar System, and of the home Elements of Astronomy in general, I refer
you to my _Clavis Cœlestis_, &c. where every thing concerning the
Planets, Comets, and Stars; and their real and apparent Motions, are
at large represented, explained, and accounted for, for the Benefit of
such as have not made the Mathematicks their regular Study.
Now, to convince you that the Planets are all in their own Nature no
other than dark opaque Bodies, reflecting only the borrowed Light of
the Sun, I must recommend to your Observation, this natural and simple
Experiment, which almost any Opportunity of seeing the _Moon_ a little
before the Full, will put into your Power to make; but best and easiest
when the Sun is in any of the North Signs, _i. e._ in _Summer_.
At such a time, the Sun being near setting, the Moon will appear in
the eastern Hemisphere; and if there be any bright Clouds northward,
or southward near her, you will plainly perceive, that the _Light_
of the one is of the same Nature with that of the other; I mean the
Light of the Moon, and that of the Cloud. To me there never appeared
any Difference at all; and I am perswaded, were you to make but two or
three Observations of this kind, which is from Nature itself, a sort
of ocular Demonstration, you cannot fail of being convinced, that the
Moon's Light, such as it is, without Heat, can possibly proceed from
no other Cause than that which illumines the Cloud: For if the Clouds,
whose Composition we know to be but a thin light Fluid, formed of
condensed Vapours only, is capable of remitting so great a Lustre, how
much more may we not allow the Moon, which, Length of Time, and many
other Circumstances, have long confirmed to be a durable and solid Body.
The Increase of her Lustre, indeed, during the Absence of the Sun from
us, to a less penetrating Genius than your's, may possibly afford some
trifling Ground of Objection to the above Conclusions, as being drawn
from the Phænomena of Day-light only; by reason in the Night, we have
no Clouds in equal Circumstances to compare with her.
But this I need not tell you, is all owing to her being seen through a
darker Medium, and not to any real Increase of natural Light emitted
from the Sun. As a Proof of which, were it necessary, you need only,
shut out the Rays of the Atmosphere, by the Help of a sufficiently
long Tube; and the Moon, or any other celestial Body, will appear
through it, as bright in the Day-time as in the Night.
Thus all light Bodies of inferior Lustre, whether shining by their own
natural Radiences, or by a borrowed Reflection, partake of the same
Advantage, when removed from the more potent Influence of a superior
one; and hence it is, that the [M]_Aura Ætherea_ shines out most
manifest, when the Body of the Sun himself is hid, the Stars, and the
_Via Lactea_ most lively and numerous in the Absence of the Moon, and
those Exhalations, or Meteors, vulgarly called Falling-stars, become
only visible (like Glow-worms) in the Night.
[Footnote M: An _Helios_, or golden Light, always attending the Sun,
and supposed to spread itself all round his Body in the Direction of
his Equator, was very visible during the total Darkness of the Eclipse
of 1715, and may be always seen about the Autumnal Equinox.]
Here it may not be improper to tell you, that the Clouds are to us in
effect no other than as so many Moons, whereby we have our artificial
Day prolonged to us several Hours after the Sun is set, and likewise
produced as much sooner before he rises; and were they to ascend by
still stronger Power of Exhalation to an Elevation, all round the
Atmosphere, so as to form a Sphere equal to four Times the Globe of the
Earth, there would then be no such Thing as real nocturnal Darkness to
any Part of the World.
The lunar Light then we may very justly conclude, proceeds originally
from the Sun: And notwithstanding many more Arguments might be drawn
from the Demonstration of her Phases, Eclipses, &_c._ to prove it,
yet none of them need here be added, to what has been already said,
to convince you of the Truth of it. This being granted, let us now
consider what Effect this, or a like Quantity of borrowed Light, would
have, when removed to a much greater Distance.
I may, I think, suppose, that you know so much of Opticks as to
understand, that all visible Objects apparently decrease in Magnitude,
as their Distance from the Eye increases. Consequently, that, if the
Moon's Orbit was placed as far again from the Earth as it really is,
her Globe, or rather _Disk_, would then seem to be but half as big
as to us she now appears to be, and of course still farther, were
she placed at ten times the Distance she is known to revolve at, her
apparent Diameter would be reduced to a tenth Part only of what it now
appears to be in her present Orbit, that is, one hundred Times less
in visible Magnitude than her neighbouring Disk is found to be where
it now is seen. And such, but something less, the two Planets _Venus_
and _Jupiter_, which are frequently, in their Turns, our Morning and
Evening Stars, appear to be through a common Telescope.
Now these two Planets, together with the other three, which we find
moving in regular Orbits round the Sun, are all found subject to the
same [N]Changes of _Phænomena_, in their various Aspects with the Sun;
and who can doubt but that they are all of the same or like Nature? But
you'll say, perhaps, how are we sure that _Venus_ and _Jupiter_ have no
native Light of their own, since many of the ancient Philosophers, and
in particular _Anaximander_, allowed even the Moon to have some; and
besides, in Philosophy, as well as in Logick, I think you hold there is
no proving a Negative, at least at such a Distance.
[Footnote N: _Venus_ and _Mercury_ in every Heliocentrick Revolution,
perform all the Changes of our Moon in a like Gradation and Defection
of Light, both horned and gibos'd.]