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Chambers, Ephraim, 1680 (ca.)-1740 / Cyclopædia, or, An universal dictionary of arts and sciences : containing the definitions of the terms, and accounts of the things signify'd thereby, in the several arts, both liberal and mechanical, and the several sciences, human and divine : the figures, kinds, properties, productions, preparations, and uses, of things natural and artificial : the rise, progress, and state of things ecclesiastical, civil, military, and commercial : with the several systems, sects, opinions, &c : among philosophers, divines, mathematicians, physicians, antiquaries, criticks, &c : the whole intended as a course of antient and modern learning
(1728)

Miserere - moon,   pp. 560-579 PDF (18.6 MB)


Page 579


( 579 )
Centre. This Equation at a mean diflance of the Moon
from the Earth, is as the Sine of the Angle contain'd be-
tween the right Line D F, and a right Line drawn from
the Point F to the Moon, nearly; and when greateft, a-
mounts to a', 25". Now the Angle comprehended be-
tween the right Line D F and a Line from the Point D, is
found either by fubfratling the Angle E D E from the
mnean Anomaly of the Moon, or by adding the Moon's
diflance from the Sun to the diffance of the Moon's Apogee
from the Apogee of the Sun. And as Radius is to the
Sine of the Angle thus found, fo is 2, 25" to the fecond
Equation of the Centre, which is to be added, if that Sine
be lefs than a Semi-circle, and fubflraaed if greater:
Thus we have its Longitude in the vcry Syzygies of the
Luminaries.
If a very accurate Computation be required, the Moon's
Place thus found mudt be correaed by a fecond Variation.
The firfi and principal Variation we have already confider'd,
and have obferv'd it to be greatenl in the Odants. The
fecond is greatefi in the Quadrants, and arifes from the
different Adion of the Sun on the Moon's Orbit, according
to the different Pofition of the AMoon's Apogee to the Sun,
and is thus computed: As Radius is to the verfed Sine ol
the diflance of the Moon's Apogee from the Sun's Perigee,
in confequentia fo is a certain Angle P to a fourth Proportio-
nal. And as Radius is to the Sine of the Moon's difiance
from the Sun, fo is the Sine of this fourth Proportional and
another Angle Qto the fecond Variation, which is to be
fubfiraiaed, if the Moon's Light be increafing ; and added,
if diminishing.
Thus we have the Mjo;o's true Place in her Orbit ; and
by redudion of this Place to rh': Ecliptic, the Moon's Lon-
gitude. The Angies P and Q   are io be determined by ob-
fervation: in the mean time, if for P be alfumed I', and
for Q i', we fhall be near the truth.
Nature of the MOON.
x. From the various Phafes of the AlMoon From her
only Jhewing a little part illumined, l 'hlat following thc
Sun ready to Let: From that Part's increafing as fhe re-
cetLs frein trn Sun, till at the diftance of SoQ She lhines
with a full Face ; ard again wains as Ihe re-approaches
that Luminary, and lofes all nur Light when fhe meets
him: From the lucid Part's being cotllantly turn'd to-
wards the Weft, while the Moon increafcs  and towards
the Ea{l when Ihe decreafes i it is evident, that only that
part fhines on which the Sun's Rays fall: And from the
Phenomena of Eclipfes, happening when the Moon fhould
Flint with a full face, viz. when ffhe is i oQ ditlant from
the Sun 5 and the darkned Parts appearing the fame inuall
Places, it is evident fhe has no Light of her owil, but bor-
rows whatever Light She has from the Sun. See PiAsES,
ECLIPsE, and SuN.
2. The Moon fornetimes difsappears in the clear Heaven,
fo as not to be difcoverable by the beil Glafles; little Stars
of the fifth and fixth Magnitude all the time remaining
vifible. This Phxnomenon Kepler ubferved twice Anno
1580, and 1583 5 and Nevelius in X6zo. Rccioli, and other
Jefuits at Bononia, and many People throughout Holland,
obferved the like April 14, 1642. yet at Venice and Vienna
The was all the time confpicuous. December 23, 1703,
there was another total Obfcuration : At Arles Ihe firmt
appear'd of a yellowiih brown; at Av.ignon ruddy and
tranfparent, as if the Sun had Ihone through ; at Marfeilles,
one part was reddifh, the other very dusky; and, at length,
tho' in a clear Sky, wholly difappear'd. Here it is evi-
dent, that the Colours appearing different at the fame time,
do not belong to the Moon; that they are occafion'd by an
Atmofphere around her varioufly difpofed in this and that
Place, for refracding of thefe or thofe coloured Rays.
3. The Eye, either naked, or arm'd with a Telefcope,
fees fome parts in the Moon's Face darker than others,which
are call'd Maculx, or Spots. Through the Telefcope, while
the Moon is either increafing or decreafing, the illumined
parts in the Maculh appear evenly terminated i but in
the bright Parts, the Bound of the Light appears jagged
and uneven, compofed of diflimilar Arches, convex and
concave. (fee Tab. ASTRONOMY, Fig. i 8.) There are alfo
obferved lucid Parts difperfed among the darker; and
illumined Parts feen beyond the limits of Illumination ;
otherintermediate onesremaining flill in darknefs; and near
the Maculm, and even in 'em, are frequently feen fuch
lucid Specks. Befide the Maculhe obferved by the An-
tients, there are other variable ones invifible by the naked
I Eye, call'd New Macular, always oppofite to the Sun;
and which are hence found among thole parts which are the
fooneft illumined in the increafing Moon, and in the decrea-
fing Moon lofe their Light later than the intermediate ones;
running round, and appearing fometimes larger, Sometimes
fmaller.
Hence, (t.) As all parts are equally illumined by the
Sun, in as much as they are equally diflant from him:
moo
'if fome appear btighter, and others darker; fome refed the
Sun's Rays more copiously than others; and therefore they
are heterogeneous. And, (a.) Since the Boundary of the
illumined Part is very fmooth and equable in the Macular;
their Surface muit bh fo too. (3.) Theparts illumined by
the Sun fooner, and deferted later than others that are
nearer, are higher than the reil, i. e. fland up above the
other Surfax e of the Moon. (4.) The New Macule an-
fwer perfedly to the Shadows of terrefirial Bodies.
4. Hezevins writes, that he has feveral times found, in
Skies perfediy clear, when even Star. of the 6th and 7th
Magnitude were confpicuous, at the latne Altitude of the
Mpoon, and the fame Eiongation from the Earth, and with
one and the fame excellent Telefcope; that the Moon and
its M.iegde do not appear equally lucid, clear, and perfpi-
cuous, at all times i but are much brighter, purer, and
more diftinct at one timne than another. From the Circum-
fiances of the Obfervation, 'tis evident, the reafon of the
Phaenomenon is not either in our Air, in the Tube, in the
Moon, nor in the Spedtator's Eye i but mutt be look'd for
in fornething exifling about the Moon.
5. Caffrni frequently obferv'd Saturn, Yuprter, and the
fix'd Stars, whn hid by the Moon, near her Limbs whe-
ther the illumined or dark one, to have their circular fi-
gure changed into an oval one; and in other Occultations
found no alteration of Figure at all. In like manner, the
Sun and Aloon rifing and fctting in a vaporous Horizon, do
not appear Circular, but Elliptic.
Hence, as we know, by fure Experience, that the Ciri-
cular Figure of the Sun and Moon is only changed into an
IEill] it one by means of the Refradion in the vapoury
Atmnain; tere, 'ris pretty apparent, that at the time when
the citcolar Figure of che Stars is thus changed by the
Moon, [ete is a denfe Matter incompafling the Moonwhere-
in the Rays emitted from the Stars are re ra6ed ; and that
at other rimes, when there was no change of Figure, this
Matter ~v'as wanting.
This Pi"aalomenon is well illufirated by the following
Experiment. To the inner bottom of any Vefel, either
Plane, Convex, or Concave, with Wax fatten a Circle; of
Paper ; then pouring in Water,that the Rays refledeld from
the Circle into the Air may be refraded before they reach
the Eye ; viewing the Circle obliquely, the circular Figure
will appear changed into an Elliplis.
6. Abe Moon is a denfe opake body, belet ewith Mountains,
Valleys, and Seas. That the Moon is denfe, and impervious
to the Light, has been fhewn : but fome parts fink below,
and others rife above the Surface ; and that coafiderably,
in as rnus h as they are vifible at fo great a diflance of the
Earth from the Sun: in the   Doon therefore are huge
lokw tains, and very  deep Val.eys.  Ricolus meafured the
height of one of the Mountains, call'd St. Catberine, and
tound it nine Miles high. Again, in the Moon are fpacious
Tradck, having fmooth even Surtaces, and thofe refleaing
lefs Light than the reft: Hence, as the Surface of fluid
Bodies is naturally even, and as when tranfparent, they
tranfmit a great part of the Rays of Light, and refled very
little ; the Lunar Spots are fluid, tranfparent Bodies:
and as they continue constantly the fame, are Seas. In
the Moon, therefore, are Mountains, Valleys, and Seas.--a
Hence again, the lucid parts of the Spots are Ijiands and
'eninftfla's.
And fince in the Macular, and near their Limbs, are feen
fome parts higher than others, in the Lunar Seas are Rocks
and Promontories.
And fince the new Spots are contiguous to the Moun.
tains, and in all refpeds like the Shadows of Bodies on
our Earth ; no doubt they are the Shadows of the Lu-
nar Mountains: Whence alfo appears the Matter of the
Moon is opake.
Note, This Reafoning will be put pafi doubt by viewing
the fenfible Horizon from fome Eminence: Where it
paffes over a Plain, the Line will appear fmooth and even;
where a-crofs Mountains and Valleys, irregular and wind-
ing; fmmooth, but dark, Lc.
7. The Moon is incompafs'd with an heavy and elafliczfr-
mofpbere, wherein Vapours and other Exhalations arife, and
whence they return in form of D)ew and Rain.
In a total Eclipre of the Sun, we find the Moon in-
circled with a lucid Ring parallel to her Periphery.
Of this, we have too many Obfervations to doubt: In
thegreat Eclipfeof 1713, the Ring was veryconfpicuous at
London, and elfewhere. Kepler obferves the fame of an
Eclipfe in J605, at Naples and Antwerp; and Wolfigs of
another in I6o6 at Leipfic, defcribed at large in the .da
Eruditorum, with this notable Circumflance, that the part
next the Moot was vifibly brighter, than that furthile from
it; which is confirmed by the Obfervations of the Frencj
Afironorers intheMemoiresdePAl'cademLe, j5c. 17o6.
Hence about the Moon is fome Fluid, which correfponde
to her Figure, and which both refleds and refraafs the
Sun's Rays. And hence alfo, this Fluid is denfier below,
ner
. MOO


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