‘ ï '44. T h é differerîtj eclipfes which may happen ó f
the moon, may .be thnsfexplained* JLet C L reprefent
the plane o f the ecliptic,' OR the moon’ s orbit, cifttiâjr
the ecliptic in*1 th^node N ' ; and le f 5# reprefent a-fee-i
tion o f the earth’ s 'fhadow at the- diftance o f the moon
from the earth,‘and M theirioon at the’ time \vhen:h? is
in bppofition to the fan7; for as the earth*s fhadow is al-
vvays oppofite tó the fun, when' the moon paffesfKy-, Or
through the fhadow, fheinuft bein oppofition. 'Mehcey i f
the opposition happen as in' portion I , it is clear that the
moon will juft pafs b y the flfèdöw ó f ^he'earth “without
entering i t a n d 'there will5 hè nó efclipfe. fÏn *pófitiön TI j
part _t>rthé raoóSivwTll*pafs îhtôugh^he-êarthV ffiâé‘o%f
and there ^ will be a partial eclipfe. J '■ In pofitión HF£We
whore ;of the -moon paffes through the earth’ s fhadow,
and there is a #ôfa/*édSpfe. jw In portion iy>* the eèntëé
o f the moon ^paffes^fhrOugh the "çeflfer o f5 the èârth?s
fhadow, and there is a fetal and central -eèliplevJ*1 I f is
'plain' therefore, that whether there' will, ^wïITtrót be
an e c lÿ fe s at the time ofoppoiïtièn, depends upon thé
diftanCfe-bfthe rnóorf f f ôfti the iiödé at "that time, ortîhé
diftance o f the'earth’ s fha^bwIroih'thé*nodè/! -Now it
appear? b y 'calculation, that^if *EiVbe gtféater th*n i i° .
3ip at the time o f «ppöfitión, there • trail'‘be vinó eèfêpfë-^
and when ENAk lefs than tha t‘*'quantity, ^tfrerc -may be
an eclipfe. ^Phe diftance '’E l f i °; 34'.) in pdfttion
I , is called the ecliptic litnfeoî a-lunar eélf|>fe. . Ör |§| ' ■
(b y the laft article ) the placé o f the earth’ s Shadow^
the fame as the place of-the earth feèfi-frOrfi the furi, It
is manifeft,=«iafcrf at the time o f oppofition we- compute
th e place o f the earth, and-find- it to be lefs than n°_
34*, from the ndde, we know that there may | be. an
eclipfe ; and then we may proceed to the calculation
but for that, We muft refer the reader to the Treatife
before mentioned, as we can here only explain the gene*
ral principles»
: ,145'. .The ' phenomena o f a- folar eclipfe, may be thus
explained. '
.iiet ^ be the fun, M the moon, ABi or A B \ prirt of
the furface o f the earth, for at different times, the earth
is at different diltarces from the moon ; draw tarigents
fxfot, gzvr, from the fun to the Jams fide o f the moon,
and«»» vrillhejth? miöon’s umbra, in whipji-no^rtof
the t fh lq a f* b b feea;r ajid<uf tangents ptkd, qtuacgbe
drawn;ftfcWhe -fun ® the/eaffih,
the fpac^ -comprehend^'d^Hetween thfe^m^a, and^w^c,
t jd r isf fcaJlçdnheptnumbfà, in which sdçly. |jpâr,t- of-the
fun cau/be Jeep., iMoW' it’ is^iianifefl:, that if A B be the
Jhrf^cfejjof'th8 earth, thejfgas« w , whererthKugj&Jffalls,
will fuffer a ■ /ato^eclipfei’s -tfef- P^t.tf* am., ,bn,. ^tw.efcn the
t ó | s pépumbra,
partial eefepfe. ; b.ut, to ,alh^tniv|ïtti<ej? ga#%tgt#)jet.e3rtih
there. wÜhl%nP, ioltpfe, .npfipayt o f the fen;tei|{g>|ftejr§
Jpâden h y th f l ip f lw J TÿW" !?f,iy'Æ\beithetffif|è^Qf
the earth,; -thçu the fp a e e« vwjl fuffer an annular and
i n appearing all round- the moon, in
the parts f t , dt, -will fuffer apartial
eclipfe ;. and the other parts o f the earth will fuffer no
eclipfe», In.jihis fituation o f the earth,, there cau there-
' fore hemp tgj^.cqligfe anywhere. ,
146. T h e umbra id s is a cone, whofe vertex b v ;
and the penumbra nuedt- is. the fruftrum o f a cone,,whofe
vertex is V , , X-lenGepif thefe be both cut through their
common axis, and perpendicular- to it, the fe&ion o f
■ .oMsJIfingig ,a common .center in the
axis, whichiisijnc linejpining the centers o f the fun and
r'topon ; and the fe&ion o f the penumbra includes that o f
.. the uuihfa.. •.
ra.7;; ^he diflerent eclipfefc wfuc^>ntay Happen o-fttiie
fun, may be tjhus expla^^k^sliet C L reprefent the o r .‘
bit a f the earth,; OR' the line defcriBed b y tbfecente«
o f .the moon’ a ambta and:p^iijmbra-at the eartjh; iiS h e
moon’ saiodeij' the earth5 f it the moonJs^enumbrai
4n4- « the umbra^ 4 The^tJM|fcfiti8n 1^. the- peuumb/a
jjitt -palfes -by the .earth,-w|lrout &9^g»opoi) it i?# ^
4^ e fe re .f eiiipfe. * t in ^ fitid n f i
penumbra falls upttiv the earth, but th.e, umbra does {not,
t$frefor& therejrwill-be a partial eehpfe’,'where the. pe-
numbra paffes over phut no total eclipfe. In .pofition
, J I I , both the ggnuntbraand umbra ftdl upon.the earth)
therefore, where the umbra gaffes o ve r ,,there will be a
total ' epiipfe 5, t where - the -»penumbras only, paffes over,-
there wlbfee a partial eclipfe } and to {the other parts oft
the earth thereViff be Mj( ecbpfe. I t ist tsapifeft therefore
that whether there will be an eolipfe, or not, or whether
it will be p'artiil qf total, depends ulpou the earth’ s diftance
from the node, at the timesof cor^u netipp. ,P*|vp w
j t appears, b y calculation, th a t, i f atrconjunCtipp, ^-bV
be greater than x7°. 2 1 there can be no eclipfe, but i f
ItJbSs le&jthcre may be one. The diftance -EiV (s=x7°,
21'), in pofition l , is-called;the itlipti?xBmti^i%#, folar.
^clipfe. 1 , iv, - -
I 148,1 ,The ecliptic limits o f the fun are to thofe or the
moon as ,17°. 21' to x i° . 34', o r ' nearly, as 3 to 2, and*
hence there will be more folart-than,'lunar eclipfes, fnj
about that "ratio.* But .more lunar than folar eclipfes, are
feen at any: given place, becaufe a, lupar eclipfe is. vifible
tq a. whole heipifphere,.o£ the earth at, once 5 whereas .a
foh»r eHipfeifs vifihte to. a'partidslyi ariitherefore there
is a greater probability of- fèang..a lunar, than a folar
ecjipfe{ ..Sinjafet,he moon is a3 long, above the hprizou
as f)h?lw5r' half :.the
;J4g. I f the earth had no atmofphere,: when'{h^^ioon
Was rotahy. eqjipfed,v IhC'.wqpldIbe invlfibfe x .hut by; the
refraftion of the atmofphere,, fotne rays, will .be brqught
tonfatt pn'th^ l0o£u’s, furface, Ipt^^which. account the
moon is repdered, viüble,: .and. of a dulky red-colour. ^
4 A n eclipfe o f the- moan .apifijig from 4 real d;e|inr
vatiop o f ,ljgfit, inujl. ap.pcar to begin at th e , fame in-
ftant.of.time to^eve^y.iplac«{on,that hemifpherp .pt^f.he
eaft51f t ó l 4iW e^-Wfi. i lP a p a rA i » jH w
method of finding, the. longitudes', p f places upon;the
i j l . T he dianieters.of.-the fun.gpil,mopn are^,fep-
pofeditp be divided into. ta e^ual,parts, called digttf^ad.
an echpfe is faid to be fo many digits, according to the
nmnber o f thofe parfs which are involved at the gteateff
darknefs. , , , . i . i f
.. , iy s . The greateft number o f eclipfes which can hap,
pen in il y'ear is feven, and when this happens, five will'
be o f the fun and two o f the moon. T he leaft number
which can happen is two,.andithe{c mull be both folar;
for in every year there muft be two folar eclipfes. | T h e
mean number in a year is about‘ four. - , u
jcq. In a total eclipfcupf die fun, the planets, arid
fpme o f the brightêft:öf the fixed fa rs, ha,vc been-feen, -
i ; u There arc two icufons in the year, when eclipfes
happe%-