-dark part of-the ipoon,. are frequently: feen enlightened
at a didanee.'.ffrpm tr^'cotiçîies'of the illuminated „part.
jTké:iàarX..parts Hàïé,"'iÉÿJome, been thought..feas ; and
-by others,, .to bte-jônjyja^reat'vnùimb^rl o f caverns .pand
4pfts,rjîte,:idârk tides r of, which . next tô the fun, - would
caufe'.thofe-.places,to appear darker than the.reft. T he .
„great irregularity o f the line bounding, the light and dark
.parts, .on every part o f the.-fipfa'cej proves thatjthere can
be.no very large.tracts o f water, as fucli 7 v 1
■ (wouldi-neceffarily produce a line, terminatiiîg'the bright
. t.partj-perfeiâly free from all'.irregularityd(T&lfoj'if;tliei e
W rnuch yvater upon-its fuifece,,and an atmofphere, as
„éonjé^üreà b y fome.adronomfers,. the cloucls, and vapours
might eafily be difcovered b y our telefcopes ; but no
..fucli phænômena.have ever been obferved. , *
Qp, Aprd^Q^’iy g y j IDpt. H e r s eg kl 'dififeÿered
feet'-;- and ‘-thatthe g'reateft height' capable -'of tefradling
the folar .rays'is yjyóffee t. adly. A t an occultation o f
jupiter’s Stellites, the third difeppeared, after having
been .i"-9K 2C M etime.n-idiftiniS; the fourth became-in-
.difceriuble mear- she limb ; this -was;,.i ot obferved- o f the '
other W ï ; ; Sëe£Üè^Pld/i riranf. . i jg z .
, i l l . Many- adrqnomers. have, given, .maps - ..of , the
moon ; 1 - 1 celebrated are-thofe of H evelius
"in- this;; Seletwgraphia ;, in which .be;,has! ireprefentëdt .the
appearance o f the 'mopn.-iii'its mirlpicnt- Jtates from -the
new to the ¥ufl,rand from the; -full. to ’ the i new; thefe
figures M ayer, prefers. ■ linn t: r r. N ir.s .and R.! cc I OL.u s -
-denoted the foots-.upon the furfece,, by .-.the ..nanies.-of .
philofophers,' mathematicians, aud pther, celebi;afed'. men;t
giving the names
three yplcànoês. in the' dark part, o f the.moon ; tw,ptp f
. th a n , u4, / ? ' almoil ex tin®,-but-the. third (bowed
-, an uftual, eruption o f fire, p r 1 u nn no us inaft e r/uefemKLuig
. afipalLpiecè o f burning çhai;çpff.çè'vëÇedLb,y a thin.içpat
, ofiyhite allies ; it. had a -degree, o f bright nds about it, as -,
ftrpng.as that with which fuch a ’ coatwpiü'd.bè Keen- to-
glow in faint d a y lig h t.T h e adjacentparts of.the volcanic
mountain fcemcd.lamtIy,( iiluniinated, by file eruption.
A fimilar .éruption .appeared - on May 4, '178.3:. . Oh
JVfarcK g, .1794-; a7fewfmin.ut.es ‘before S. o’ clockyihrjthey
, evening,. M ^ ! ^ ilk’ins o f Norwich, an! eminent, archi- '
. te d , obferved, with the naked e y e, a very .bright, fpot
upon the .dark.part o f the moon ; it was .there when jje
firftlooked at the moon ; and the .whole time b e faw it,
.which was about y minutes, i t was .a fixed, deady fight-,
. .except;, the moment. - before it.'drfappparcd, • when ffs/
brigfitnefs .inçreafeib'.' T he famé“ pjimnôinenonf^sbalîb .
. obferved by ( M r. T . Stre t to n, in St. .John’üqù'àré,
Clalcefiwieli, LondonL On A p r il’13ƒ 1793, M. P ia z z i ,
Afirphomer-iR.oyal, at-. Palermo, .obferved. a. bright fppt
i&nStbe. dark ‘part o f thÿmppn pand'feveraXqthef.adrbno- .
mers have obferved the fame pHiehomenon. ,
I to . I t .has been./-a ;doubt„.. ahiongd yaftronomers, ■
whether the moon has any atmofphere ; dome füfpeéting ■'
that at ap occultation ofi-a fixed dar b y ‘th e moon, the ■
- Aar did not yànifeîudàénlÿ, B u tlo d its^fight' gradnally, '
and thence xoncluaed, that, theymodfi;has ; an atmofphere.
M. .SchroIeter lof iLilionthau, in the Dùtchy of. .
Bremen ',, has erideayoured to eflablifii theexiftence'of an
atmofphere,Vfrqmfthe\ following- ôbfervàtions.’ ‘ i . He
obferved the moon when 2+ days old,; in the .evening '
foon after fun fet, before the dark part Was vifible ; arid I
continued to obferve it till it became viliblêf Tw o cufps
.appeared tapering in. â very fharp, feint prolongation,
each Kthioiting its far the (l extremity faintly illuminated
b y thé fôlar rays', befpre'-any pa rt o f the dark Hemisphere
was vifible J foon after, thé whole .'dark limb'^peàred-il-
laminated.' This prolongation o f thecufps'beyoridithe
femicircle, he thinks muft arife from the fun’ s rays being
refrâéVed b y the moon’s atmbfphere. He computes alfo
the height pf’tHe atmofphere, which rëfrafts fight enough '
intb'thc dark hemifphëre to produce a. twilight,'more '
lumifi!qus.,than the light reflected. from- the earth when 1
i)ié‘ 'ùidon is about 320 frô jn th ï newj‘ -to be ^'3376 pans
the- earth. The former
diitindiion fe-now generally ufed.
, i 12. i^l| ■ „ ■ >. , moon is always
niyred.lp.wavdsuju: .eartb.bd-.being, fulljedl. I-o-only a fmall -
change wn.lun certainblimi-ts; 'tbofe.fpots .which lie,.near
s^fytjyns,,;: this is
called, its ] ,ïbratnm,, T h e mdpift-.iirh s!1 about its- axis in *’
-the paine ferêftmn-.imwHemit; : Now
tl-.e angular, velocity ^bdut'-its;;axis is 'uniform!, 1 and/"it
turps about its axis Jn the, fanie time in■! " '' i ri 1- k l '! 1
.complete revolution in its orbit ; i f therefore, tlrbna’ngu-;
lar motion abpjjt,the earth were-alfo ninform,-the fame
fece -bf, the mooU;„wouia ^tyays- m e ^ r ,u ed ^ w a rd it^ e .
earthy -Igor.if .the inoon had ^^^omtijm.oji her axis,
when (he.is on oppofite fides ,qf. the earth- flic wótild Ihow *
.fijfféreritfeces;. but if, after (he I , , 1 iyevolu- •
SBlffikm. A .
axis,, tlieii, the tune, .wliidl S i y 1 *
filown,"iyillbe tiirried behind',and’t{ie fa-m'e^fece'gyill appear.
- A r id , thus :df tho,mppri|'R angular velocity ^ about t
her Jaxisiws^always.ëqüai.'jo bci angular velocity in.her;
tólb’ittabóut We'.ëarfH. .the^fame^de'pf tlie'ino.onnwould
be always^ tos.wp.rds the earth.- But asr-the . i _ .
lar.velocity ubou! her.axis:is uniform, band-'hei-'angular '
velocity in her'orbit is not;ü.nfför-m^ ;^'ei#R-pguigr .velocities
cannot, continue.always,equal, _a'nd uieiefore,„111 e
moon-, .’will 'fométimes'Ihovy a fifctle'eió'pre pf'ber'. cail- ■
em;^ r^ Sjf an.d’Jpmfe'imés.:.a'fihle;rpêïeljbf lieri wcftern
pa rts;. this is- cqllefiga, libfation vAJongftuae'., ,Aifp|j the
mOph’ s-aiis is not perpe-ndipul^i; tpbthé plane-ho-f liex or- '.
bit, and’ .her-'"
opppfifè.'pbïes hré .'t.uTóiéd towards; t l S e arthy therefore
hër-pólês appear, auigdifappeaiy by'turns j this caUed a
libra turn -in latitude,.
113. H ence;'nearly one, Kalf o f
vifible at the earth, ah3'j®erefpre^Jimarlyipne.balfJof .its -
inhabitants ( if jt have * anyy-g-never -few ’the earth ,' .'and
nearly the other half nèycr|loföï light o f it, A lfo , -t(ie
time psf j^ -ïp t^ n L a k q u t^ fji mti» the
(length c f ; :ie jfir.ar days 'and nights will .'bepbputtfa
fortnight each. ' „'
1 1_4- I t is ia ’.vèi^ jSiijprdiiiary' eircumfl^P1;?« ■ that
the time1 (of the'- hyc!ion’Vfevolution abb-u.t lieig.a-xie jhould
be equal to ".that iii hér oftiiti” 'S ib. 1 ."N e k t o n ,‘ ïróm!
the
1 1
LIl
the -altitude o f the tidcs upon the earth, has computed the
.altitude of. the. tides bn the MoWs fe febe tB be 93 feet,
jvnd,thej^fere^hevdjameterxjfithe mobh.pt%jenJicplaFto
a (hne joiniug. the eajith^anfinmdoji, isviefs’ lShan thPcfia-
raeter direfted.to'.theieBrth/by -»$5 feet.1 <»iHttc(i',h%s
he, the fame face muft always’ -be towards the earth, e xcept
a fmall dfciUationv; fqv-. i f the lorigeft 'dia in^r
-feouM gefea) litf-losou^esf tha^reiaidfife.S'tf-WQ-^'a: he
■ brought mto it again, by the earth’ s attraaion. The
fuppohtion o f D . DE-iM -t r R A n .is;- 'that the ltemi-fpliek
o f the moon next the earth is.mdre.'denfe than the ap-
pgfite one, and licnue, ithe 1 feme dacti’-Wo-'uld be k e p t to-
«iardj thefeart-h, upon the fame principle as before,
«■ i^J. AVHenatlic m(,a.iriwin co qq i-iSflwy(itlnthl &A,
1S then faid to be new, M S her dasik-fide beino- next
’to th e d rife,Tffit’ 1-1 rtkn iii.-LHibfe. - \ lf lp # ^ d e s^ & m
-the fun, aid;'.
flit, appears- horned
fee ,appea s half ei.ligffii.ncd,7irfc<*#/ I’ ltr tltl i^'fram
thence, tjll il c, c. orm.-' mto «pjR fition, Wn apgf ws above
h^fjenii&btfenejliior ^rAi6iw';saifilI^ 'S o p p ) t^ i*M g ‘ap-
peats full - orb'edj-ctjifti lame face being then turned towards
the earth which
f|{d1itoibe.wt'herj&& Addfedm oppefitidh trf>co.#rn!;-
W&z .-h#f ^ p a r e B t eM g h t^ t . ' t e r ^ ^ a ‘t i i t % « i r iii[4
- etW?-; ^Khemthe'inoopiis about t hre c- days fro ITU t he:rfc iv,
-Wltsartfik-which..fiiil nww n-'E^Ht' - tpr th l' luiftffiaii^, -feiiifi-
denag u|i;Ssartlv as a mepiv to' »the WbK
feyp.urldde -ftaU*, xfdnte;Pf„ tile fpotsmay be-hh'en'diieii.
-B ut wbemthemforni gets itttd;quadrat<Crfc87«itslgfeatlight
.preyentstbe dark part frombeing feenVt^g^ffig;rtr’D^.
.Sjft’ Tf«* the .ftfoi^th o f moomUght a©.the
oQ-t-hpufend times fefc tban the-ligbt-;«the-fun • Blit
fromexpefhnentB- mlde by M . Bpti &®M.^efconelfided
■ it tq,‘be,,3^e thoufend' times lefs. hyei|ght:'o 'f 'the
$opn, coudeufed-by. the’beft mfirOrs, ■ prodSdils'riolfetf-
fible effefe upoh. the thmimbmeteS -^OurJ ^f^?ii®SWe-
epurfe o f a month, Ihdwsdhe feme-phafCs to- the-Htharl-
ans, as the.moon does^to '.n&j! the earth-is at ftfe-fte.Ttt
,the tiip'e EPs;the new moon, an'd ar-neWi- at-'die tifric of'
th,e,full mp.on. T he furfece oflthe ehrfh bOm w
S im a greater than; that Ofitlic' moon, it' affords f.^itih^s
,mpre light to the moon, «ban the« mpon'dbes to‘u s .' ! !
t f j , JiRj H sa seH E t -has meafured tfee 'hft’gliit'of'a
great many of^he lunar mountain«, andrfmds that,*a few
l«iceept.e4 they genaraliy do
mile, Befprp he. meafured . thefe)- thaw1-were •feckmiVd
being ,ge»erally, overrates. li^Jbbf#y4 ,
.that it feould be exsamined -whether tfeie «ofeifam ft'ands
on- level ground, which is heceffaif, -th&t thC meafurt-
jneqt map be„exabf. x
• , -1 1®'. A s the fpe^tator. is- carri.ed b y the earth's rota-
bpn, his horizon will otartanaall-y Vehahge its^fithatffefi,
and therefore it wiUbomanurfl.y:
”Sierunt' f<)i?,:S *^^t'ha8g'qnethrb'ugh1thewhole bfhft;
and tpe .mpltnation of-the orbit -to.'the-lioriz'oir Will be
continually changed. Now t-he differenee between the
TOE. 1» ,
'pf the 1-ifing o f the moon on two" feiccéffive
nights, will depend'upon the angle which the moon’ s
orbit makes Wilh the horizon '; the (lefs the angle is,
the- defs tne moon will have defeended below the ho-
nzon. at lhe‘ time’ When the ‘horizon is brought into
the feme fituation it was 24 hours before; therefore
when th e ' angle which the moon’s orbit makes
with the horizon 'is the-leaft, there will be the leak difference
o f the times o f her riling. Now, that angle is the
lë&ftj when the firft point pf'aries rifes, at which time, in
latitude o f London, there is only about 17 minutes dif-
1 -fcrcnce of- the moon’ s riling on two fuccelfive nights.
Now, about the 22'd o f September, the firli point o f
aries rifes at the time the moon rifes, i f the moon be
then a t the full, becaufe it will then be at the beginning
o f aries. In this cafe, therefore, the moon will rife about
the full for.feveral nights, .with but a fmall difference o f
‘She times o f her tiling. This happening iii the time o f
liarveft, it is called the havvejl moon. ’ A s the full moon
" may not happen on the'22d o f September, that which
happens neared to it, is called theharveft moon. The fame
fn&Ii difference o f the times ‘o f riling o f the moon, happens
every month, but it not happening at the full
■ n?oon> an^ at that time o f the yèar, it is not taken no-
tiéd^èP T hé greatéft difference o f the times o f the
moon’s nfing atr Lotièlotf ón IWo iiiccelfive - nights, is
about 1 hour and; 17' minutes; arid this happens when
• the rrioon is in the fil'd point o f libra, and therefore it
•happens >4t th e vtmal M ifeöönè.' ' ’
^ .pfiiëödmenoj - cdlfpd'tlie horizontal
mook,-which is thisj that it appears larger in the horizon
than in the meridian; whereas, from its being farther from
léf*
Hvlieii m ‘tIiidh6ri2on,i I t is/perhaps not efify to
give-'a felisfectory anfvèèr t&'ftuS .deception. G assen-
-DU s;fhduglft tlfet, as fhe fe^omwa« 'lefs bright in the
' h‘c>ri/óixthan in tlié liffe|id^rf,;vv'p looked at; ft, in the
■’®|®e^ M f a ^ l | * (gfeiéêri eye, and
tHerefore it appea*d' fei’gir.“ ' But this isf not agreeable
^•th e l> N h c i® ^M ® S S v&ce,tbfemagnitude p f the
image upon'thè'ïetifta’p fïS eh y e, ‘does not depend upon
khe®2e-6f)A/;pgpiI.i|J^s/Ciia2-E's thought thatthe
moqnlIÉppeftieaHferg» becaufe, when
T t l i t ; , r a t e r m e d i a t e objeffe, it
greater)'p tha t iMatipn we, o/póqrfe, think it larger,
fuppdfing that it fpbténds the feme angle. D r. Berkley
accounts fór it thus : . Faintnefs fuggeds the idea
o f greater didance ; the imppn appearing feirited in the
horizon, fuggeds- the idea o f greater didance ; and, fup-
pofing the angle die famey that mud fugged the idea o f
a -,greater tangible objeft. , He .does;.not fuppofe the
t-9;b;e greater, but. that , the, idea ó f a -
greater tangible exlénfion is fuggeded, by the alteration
o f the .vifible ex.tenfionV, He „fays,— ill, That which
idea pf greater magnitude, .'mud be fomè-
(tbJngbgiSserved; for that which is nol pirceivéd can
produce no effeift.; ;.2dljr,' i t mull hé. fomediing.-which.
« .variable,' becaufe the moon does dot always appear o f