Page:Cyclopaedia, Chambers - Volume 2.djvu/228

 MOO

( TO )

MOO

Centre. This Equation at a mean diftance of the Moon If fome appear brighter, and others Hart,.,-. r„™»,.ri,,A i. from the Earth, is as the Sine of the Angle contain'd be- Sun's Rays more -- >rker ; fome refletf th,

twecn the right Line D F, and a right Line drawn from

the Point F to the Moo», neatly ; and when greatefi, „ mounts to 2', 25". Now the Angle comprehended be- tween the right Line D F and a Line from the Point D, is found either by fubftracting the Angle E DE from the

mean Anomaly of the Moon, or by adding the Moon's other Surfa e of the

copiouily than others ; and therefore they are heterogeneous. And, (2.) Smce the Boundary of the .Hummed i art is very fmooth and equable in the Macular. their Surface mull be fo .00. (3.) The pans illumined by the Sun iooner, and deferred later than others that are nearer, are bigner than the reft,

e. Hand up above the

jnean ni^-j «• "n- j«™, or oy aamng the Moons otner ourta e ot the Moon f 4 ) fhe \'r» M 1

diftance from the Sun to the diftance of the Moon's Apogee fwer perfectly to the Shadows .of terreftrial Pot) from the Apogee ot the Sun. And as Radius is to the 4- ««*« writes, that he has feveral rim..*. J -

Sine of the Angle thus found, fo is z", 25" to the fecond Sk.es perfectly clear, when even Star of the Irhn' k

Equation ol the Centre, which is to be added, if that Sine Magnitude were confpicuous at the lame Altit d F K

be lefs than a Semi-circle, and fubftraaed if greater : Moo,,, and the fame Elongation from the Earth and w^th

Thus we have its Longitude in the very Syzygies of the one and the fame excellent Telelc

,, that the Moon and its Macula do not appear equally lucid, clear, and perfpi* cuous at all times; but are much brighter, purer and more dittinct at one time than another. From the Circum- stances ot the Obfervation, 'tis evident, the reafon of the Ftenomenon is not either in out Air, in the Tube, in the Moon, nor in the Spectator's Eye ; but mull be look'd for in lomcthing exilting about the Moon.

5. Cafini frequently obferv'd Saturn, Jupiter, and the fax d Stars, when hid by the Moon, near her Limb, whe-

Luminaties.

If a very accurate Computation be required, the Mum's Place thus found mull be correct ed by a fecond Variation. The firil and principal Variation we have already coniider'd, and have obferv'd it to be greatefl in the Octants. The fecond is greatefl in the Quadrants, and atifes from the different Action of the Sun on the Moons Orbit, according to the different Fofition of the Moon's Apogee to the Son, and is thus computed : As Radius is to the vetfed Sine of

the diftance of the Moon's Apogee from the Sun's Perigee, ther ihe illumined or dark one, to have their circular Fi mconfequentiafois a certain Angle P ,0 a fourth 1'roportio- gure changed into an oval one ; and in other Occultations nal. And as Radius is to the Sine of the Moon's diftance tound no alteration ot Figure at all In like manner the from the Sun, fo is the Sine of this fourtn Proportional and Sun and Moon rifing and letting in a vaporous Hor.Vnn An another Angle Qjo the fecond Variation, which is ro be -»» .™.. n:.,..i.l fubhtacfed, it the Moon's Light be increaftng ; and added, if diminishing.

Thus we have the Moon's true Place in her Orbit ; and by reduction ol this Place 10 the Ecliptic, the Moon's Lon- gitude. The Ar.gies P and Qare >u be determined by ob fervation : in the mean time, it {or P be affumed a', and for Q_ 1', we fiiall be near the truth.

Nature of the Moon. 1. From the various Phafcs of the Moon : From her on!) fhewmg a little patt illumined, 'hen following the Sun ready tp let : From that Part's increaftng as fhe re- cedes from tiftJ'Snri, till at the diftance of 8o Q fhe (nines with a Full Face ; ami again wains as Ore re.approac.hes that Luminary, and lofes ail ier Light when (he meers him : From the lucid Part's being cpnftantly turn'd to- wards the Weft, while the Moon increaXesj and towards the Eaft when (he decreafes ; it is evident, that only that part fhines on which the Sun's Rays fall ; And from the Phenomena of Eclipfes, happening when toe Moon Jhould fhme with a full face, ok, when fire is iso° dittant from

the Sun ; and the darkned Parts appearing the fame in all Earth from th'e~Sun : In the Vfc,» thetefore are f Places, ins evident flie has no Light of her own, bur bor- Morten,, m A „ ery i, e? Valleys. Riccohs iwsafured E rows whatever Light (he has from the Sun. See Phases, height of one of the Mountains, call'd St. lather, ne and T^'m r UN '' XT ■ u, o Jound it nine Miles high. Again, ,n the Moo* are fpaciV us

2. TheMooBfometimesdifappeats in the clear Heaven, Traflr, nav.ng linooth even Surfaces, and thofe refleftint. fo as not to be recoverable by the befl Glaffes ; little Stars lefs Light than the reft = Hence, as the Surface of fluid

not appear Circular, but Elliptic.

Hence, as we know, by fure Experience, that the Cir- cula. figure ot the Sun and Moon is only changed into an K.Uiptlcone by means of the Refraaion in the vapoury Atmofphere > 'tis pretty apparent, that at the time when the cucular Figure ot the Stars is thus changed by the Moon, tne,e is a denle Matter mcompaffing the /VW.where- in the : Rays emitted from the Stars are refrafled ; and that at other times, when there was no change of Figure, this Matter was wanting.

This Phenomenon is well illuftrated by the following Experiment. To the inner bottom of any Vcffel either Plane, Convex, or Concave, with Wax fatten a Circle of Paper j then pouring in Water.that the Rays reflected from tne Circle into the Air may be refracted before they reach the Eye ; viewing the Circle obliquely, the circular Figure will appear changed into an Elliptis.

0. lie Moon is a tienfe ofake EoJy, lefet with Mountain; Valleys, and Seas. That the Moon is denfe, and impervious to the Light, has been (hewn : but fome parts link below and others rife above the Surface ; and that confiderably' in as mu. h as they are viftble at fo great a diftance of < he

of the fifth and iixth Magnitude alt thi vifible. This Phenomenon Kepler obferved twice Anno 1580, and 1583 5 and hlevel'ms in 1620. Riccioti, and other Jefuits at Hononia, and many People throughout Holland obfetved the like April 14, 1642. yet at Venice and Vienna fhe was all the time confpicuous. December 23, 1703, there was another total Objuration : At Aries (lie tlrlt appear'd of a yellowifh brown ; at Amotion ruddy and

time remaining jtfodie. is naturall

y even, and as when tranfparenr, they tranfmit a great part of the Rays of Light, and reflefl very little ; the Lunar Spots are fluid, tranfparent Bodies : and as they continue conllantly the fame, are Seas. In"

the Moan, therefore, are Mountains, Valleys, and Seas

Hence again, the lucid parts of the Spots are 1/lands and Feninjula's, And ftnee in the Macula-, and near their Limbs, are feen tranlparent, as if the Sun had (none through : at MarfeiUes, fome parts higher than others, in the Lunar S-as ar- Rods one part was rcddiln, the other very dusky ; and, at length, and Promontories.

tho' in a clear Sky, wholly difappear'd. Here it is evi- And fince the new Spots are contiguous to the Moun dent, that the Colours appearing different at the fame time, tains, and in all refpefls like rhe Shadows of Bodies on do not belong to the Mooh ; that they are occafion'd by an our Earth; no doubt they are the Shadows of the Lu Atmofphere around her varioufly difpofed in this and that nar Mountains : Whence alfo appears the Matter of the" Place, for retracting ot thefe or thofe coloured Rays. Moon is opake.

3. The Eye, either naked, or arm'd with a Telefcope, Note, This Reafoning will be put pad doubt by viewine iees fome parts in the Moon's Face darker than others,which the fenfible Horizon from fome Eminence- Where it are call'd Macula:, or Spots. Through the Telefcope, while paffes over a Plain, the Line will appear fmoorh and even - the Moon is either increafing or decteafing, the illumined where a-crofs Mountains and Valleys, irregular and wind' parts in the Macula: appear evenly tetminated ; but in ing ; fmooth, but dark, Jt?c.

the bright Parts, the- Bound of the Light appears jagged 7. The Moon is incompafs'd with an heavy and elaltic At- and uneven, compofed of diflimilar Arches, convex and moffhere, wherein Vapours and other Exhalations arife and concave. (Tee Tab. Astronomy, Fig. 18.) There are alfo whence they return infirm of Dew and Rain. obferved lucid Parts difperfed among the darker ; and In a total Ecliple of the Sun, we find the Moo« in. illumined larts feen beyond the limits of Illumination ; circled with a lucid Ring parallel to her Periphery othermtermediate onesremaining ftill in darknefs ; and near Of this, we have too many Obfervations to doubt ■ In the Macula-, and even in 'em, are frequently feen fuch thegreat Eclipfeof 1713, the Ring was very confpicuous at lucid Specks. Betide the Macula: obferved by the An- London, and elfewhere. Kefler o'bferves the fame of an ticnts, there are other variable ones invifibleby the naked Eclipfe in 1605, at Naples and Antwerp ; and Wolfius of • Ey e > "''' d lNew Macula-, always oppofite to the Sun; another in 1606 at Leipfic, defcribed at large in the ABa and which are hence found among thofe parts which are the Eruditorum, with this notable Circumftance, that the part fooneft illumined in the increafing Moon, and in the decrea- next the Moos was vifibly brighter, than that furtheft from fing Moon lofe their Light later than the intermediate ones ; it ; which is confirmed by the Obfervations of the French running round, and appearing Sometimes larger, fometimes Aftronomers in the Memoires del' Academe, i£c. 1705. fmaller. Hence about the Moon is fome Fluid, which correfponds

Hence, [%.) As all parts are equally illumined by the to her Figure, and which both reflefls and refracts the Sun, in as much as they are equally diftant from him : Sun's Rays. And hence alfo, this Fluid isdenfer below