ASTRONOMY. - 397 
globe, only that half of it, which at any time is turned 
towards the Sun, can be enlightened by him at that time; 
it is upon fome part of this enlightened half of the Earth 
that the Moon’s lhadow falls in a folar eclipfe. 
The Sun is always in the plane of the ecliptic ; but the 
Moon being inclined to this plane, and only coinciding 
with it at the nodes, it will not cover either the whole or 
a part of the Sun, or in other words the Sun will not be 
eclipfed, unlefs the Moon is in or near one of her nodes. 
The Moon, however, cannot be direCtly between the Sun 
and us, unlefs they are both in the fame part of the hea¬ 
vens ; that is, unlefs they are in conjunction. Therefore, 
the Sun can never be eclipfed but at the new Moon, nor 
even then, unlefs the Moon at that time is in or near one 
of her nodes. From hence it is eafy to (hew, that the 
darknefs of our Saviour’s crucifixion was not owing to an 
eclipfe of the Sun. For the crucifixion happened at the 
time of the Jewifh paffover; and the palfover, by the ap¬ 
pointment of the law, was to be celebrated at the full 
Moon ; the Sun could not, therefore, be eclipfed at the 
time of the paffover. 
The Moo'n being much fmaller than the Earth, and 
having a conical fhadow, becaufe (lie is lefs than the Sun, 
can only cover a fmall part of the Earth by her (liadow ; 
though, as we have obferved before, the whole body of 
the Moon may be involved in that of the Earth. Hence 
an eclipfe of the Sun is vilible but to a few inhabitants of 
the Earth ; whereas an eclipfe of the Moon may be feen 
by all thofe that are on that hemifphere which is turned 
towards it. In other words, as the Moon can never to¬ 
tally eclipfe the Earth, there will be many parts of the 
globe that will fufter no eclipfe, though the Sun be above 
their horizon. An eclipfe of the Sun always begins on 
the wefiern, and ends on the eaftern, fide ; becaufe the 
Moon, moving in her orbit from weft to eaft, neceffarily 
firth arrives at and touches the Sun’s weftern limb, and 
goes off at the eaftern. 
It is not neceffary, in order to conftitute a central eclipfe 
of the Sun, that the Moon (hould be exactly in the line 
of the nodes, at the time of its conjunction ; for it is fuf- 
ficient to denominate an eclipfe of the Sun central, that 
the centre of the Moon be dire« 5 tly between the centre of 
Sun and the eye of the fpeCtator ; for to him, the Sun 
is then centrally eclipfed. But, as the (liadow of the Moon 
can cover but a fmall portion of the Earth, it is obvious 
this may happen when the Moon is not in one of her nodes. 
Further, the Sun may be eclipfed centrally, totally, par¬ 
tially, and not at all, at the fame time. Thus, in fig. 7, 
of the Aftronornical-Plate V, let ABC be the Sun, MN 
the Moon, klg part of the cone of the Moon’s (hadow,_/^ 
the penumbra of the Moon : from this figure it is eafy to 
perceive, 1. That thofe parts of the Earth that are with¬ 
in the circle reprefented by gh, are covered by the (liadow 
of the Moon, fo that no rays can come from any part of 
the Sun into that circle, on account of the interpofition 
of the Moon. 2. In thofe parts of the Earth where the 
penumbra falls, only part of the Sun is vilible ; thus be¬ 
tween d and g the parts of the Sun near C cannot be 
feen, the rays coming from thence towards d or g being 
intercepted by the Moon ; whereas at the fame time, the 
parts between f and A are illuminated by rays coining from 
C, but are deprived by the Moon of fuch as come from 
A. 3. The nearer any part of the Earth, within the pe¬ 
numbra, is to the (liadow of the Moon, as in places near 
g, l, or h, the lefs portion of the Sun is vifible to its inha. 
bitants ; but the nearer it is to the outfide of the penum¬ 
bra, as towards d, or f, the greater portion of the Sun may 
be feen, 4. Out of the penumbra, the entire dilk of the 
Sun is vifible. 
The Moon’s dark (liadow covers only 3 fpot on the Earth’s 
fur face about 180 Englifli miles broad, when the Moon’s 
diameter appears larged, and the Sun’s lead; and the to¬ 
tal darknefs can extend no farther than the dark (liadow 
covers. Yet the Moon’s partial (liadow or penumbra may 
cover a circular fpace 4900 miles in diameter, within all 
V91.. II. No. 78. 
which the Sun is more or lefs eclipfed, as the plac.es arc 
lefs or more diftant from the centre of the penumbra. 
When the Moon changes exaCtly in the node, the penum¬ 
bra is circular on the Earth at the middle of the general 
eclipfe; becaufe at that time it falls'perpendicularly on 
the Earth’s furface : but at every other moment it falls 
obliquely, and will therefore be elliptical ; and the more 
fo, as the time is longer before or after the middle of the 
eclipfe ; and then much greater portions of the Earth’s 
furface are involved in the penumbra. When the pe¬ 
numbra firft touches the Earth, the general eclipfe be¬ 
gins ; when it leaves the Earth, the eclipfe ends: front 
the beginning to the end the Sun appears eclipfed in 
fome part of the Earth or other. When the penum¬ 
bra touches any place, the eclipfe begins at that piace, and 
ends when the penumbra leaves it. When the Moon 
changes in the node, the penumbra goes over the centre 
of the Earth’s dilk as feen from the Moon; and confe- 
quently, by defcribtng the longed line polfible on the 
Earth, the Sun’s general eclipfe continues the longed up¬ 
on it ; namely, at a mean rate, 5b. 50m. more, if the 
Moon be at her greateft didance from the Earth, becaufe 
(he then moves llowed; T&fs, if die be at her lead didance, 
becaufe of her quicker motion, as obferved before in 
eclipfes of the Moon. 
A total eclipfe of the Sun is a very curious phenome¬ 
non ; and, as there are not many perfons who can have an 
opportunity of feeing one, we dial 1 here give the particu¬ 
lars recorded of that which happened on the 22d of April, 
1715. Captain Stannyan, at Bern in Switzerland, fays, 
“ the Sun was totally dark for four minutes and an half; 
and that a fixed dar and planet apeared very bright; and 
that its getting out of the eclipfe was preceded by a blood- 
red ftreak of light from its left limb, which continued 
not longer than lix or (even feconds of time ; then part of 
the Sun’s dilk appeared all on a fudden, as bright as Ve¬ 
nus was ever feen in the night ; nay brighter, and in that 
very inftant gave a light and fhadow to things, as ftrong 
as Moon-light ufed to do.” The inference drawn from 
thefe phenomena is, that the Moon has an atmofphere. 
J. C. Facis, of Geneva, diys, “ there was feen, during, 
the whole time of its total immerfion, a whitenefs, which 
feerned to break out from behind tiie Moon, and to en- 
compafs it on all ddes equally ; its breadth was not the 
twelfth part of the Moon’s diameter. Venn's, Saturn, 
and Mercury, were feen by many ; and, if the Iky had 
been clear, many more ftars might have been feen, and 
with them Jupiter and Mars. Some gentlewomen in the 
the country law more than (ixteen liars; and many people 
op the mountains faw the ficy darry, in fome places where 
it was not overcaft, as during the night at the time of the 
full Moon. The duration of total darknefs was three 
minutes.” Dr. J. J. Schenchzer, of Zurich, fays, that 
“both planets and fixed ftars were feen ; the birds went 
to rood ; the bats came out of their holes ; and the fillies 
(warn about; we experienced a manifed fenfe of cold; 
and the dew fell upon the grafs. The total darknefs laded 
four minutes.” 
Dr. Halley, who obferved this eclipfe at London, has 
thus given the phenomena attending it. “ It was univ'er- 
fally obferved, that, when the lad part of the Sun remained 
on its eaft fide, it grew very faint, and was ealily fupport- 
able to the naked eye, even through the telefcope, for 
above a minute of time before the total darknefs; whereas 
on the contrary, my eye could not endure the fplendaur of 
the emerging beams in the telefcope from the fird mo¬ 
ment To this perhaps two caufes concurred ; the on?;, 
that the pupil of the eye did neceffarily dilate itfelf during 
the darknefs, which had before been much contracted by 
looking on the Sun. The other, that the eaftern parts of 
the Moon, having been heated with a day near as long as 
thirty of ours, mud of neceffity have that part of its at¬ 
mofphere replete with vapours, railed by the long-cu.nti- 
nued action of the Sun ; and by coiifequ'ence, it was mor e 
denfe near the Moon’s furface, and more capable of ob_ 
j I ftfuCtin 0 . 
