39 S ASTRO 
ftrudtin'g tlie 1 nitre of the Sun’s beams. Whereas at the 
lame time the weftern edge of the Moon had fuffered as 
long a night, during which time there might fall in dews, 
all the vapours iliat were raifed in the preceding long day ; 
and for that reafon, that part of its atmofphere might be 
feen much more pure and tranfparent. About two mi¬ 
nutes before the total immerfion, the remaining part of the 
Sun was reduced to a very fine horn, vvhofe extremities 
deemed to lode their acutenefs, and to become round like 
ftars. And, for the fpace of about a quarter of a minute, 
a fmall piece of the fouthern horn of the eclipfe feemed 
to be cut off from the reft by a good interval, and ap¬ 
peared like an oblong ftar rounded at both ends: which 
appearance could proceed from no other caufe but the 
inequalities of the Moon’s furface, there being fome ele¬ 
vated parts thereof near the Moon's fouthern pole, by 
which interpofttion, part of that exceedingly-fine filament 
of light was intercepted. A few feconds before the Sun 
was totally hid, there difcovered itfelf round the Moon a 
luminous ring, about a digit or perhaps a tenth part of the 
Moon’s diameter in breadth. It was of a pale whitenefs, 
or rather pearl colour, feeming to me a little tinged with 
the colours of the iris, and to be concentric with the Moon ; 
whence I concluded it was the Moon’s atmofphere. But 
the great height of it, far exceeding that of our Earth’s 
atmofphere ; and the obfervations of fome who found the 
breadth of the ring to increafe on the weft fide of the 
Moon, as the emerfton approached ; together with the 
contrary fentiments of thofe, whofe judgment I (hall al¬ 
ways revere; make me lefs confident, efpecially in a mat¬ 
ter whereto I gave not all the attention requifite. What¬ 
ever it was, this ring appeared much brighter and whiter 
near the body of the Moon than at a diftance from it; 
and its outward circumference, which was ill defined, 
feemed to terminate only by the extreme rarity of tlie mat¬ 
ter it was compofed of; and in all refpefts refembled the 
appearance of an enlightened atmofphere viewed from far : 
but whether it belonged to the Sun or the Moon, I fliall 
not at prefent undertake to decide. 
“ During the whole time of the total eclipfe, I kept my 
telefcope conftantly fixed on the Moon, in order to obferve 
what might occur in this uncommon appearance, and I faw 
perpetual flaflies or corufcation of light, which feemed 
for a moment to dart out from behind the Moon, now 
here, now there, on all (ides, but more efpecially on the 
W'eftern fide, a little before the emerfion : and about two 
or three feconds before it, on the fame weftern fide, where 
the Sun was juft coming out, a long and very narrow ftreak 
of a dufky but ftrong red light feemed to colour the dark 
edge of the Moon, though nothing like it had been feen 
immediately after the immerfion. But this inftantly va- 
11 ifiled upon the firft appearance of the Sun, as did alfo 
the aforefaid luminous ring. As to the degree of dark¬ 
nefs, it was fitch, that one might have expected to have 
feen many more ftars than were feen in London ; the pla¬ 
nets, Jupiter, Mercury, and Venus, were all that were 
feen by the gentlemen of tlie Society from the top of their 
houfe, where they had a free horizon : and I do not hear 
that any one in town faw more than Capella and Aldebaran 
«f the fixed ftars. Nor was the light of the ring round 
the Moon capable of effacing the lu fire of the ftars, for it 
was vaftly inferior to that of the full Moon, and fo weak, 
that I did not obferve it eaft a ftiade. But the under parts 
c>f the hemifphere, particularly in the fouth-eaft under 
the Sun, had a crepulcular brightnefs ; and all round us, 
fo much of the fegment of our atmofphere as was above 
the horizon, and was without the cone of the Moon’s 
fiiadow, was more or lefs enlightened by the Sun’s beams; 
and its reflection gave a diffufed light, which made the 
air feem hazy, and hindered the appearance of the ftars. 
And that this was the real caufe thereof, is manifefted by 
the darknefs being more perfect in thofe places near which 
the centre of the ftiade pafted, where many more ftars were 
feen, and.in fome, not lefs than twenty, though the light 
of the ring was to all alike. I forbear to mention the 
N O M Y. 
chill and damp, with winch the darknefs of this eclipfe 
was attended, of which molt fpedfators were fenfible, and 
equally judges ; or the concern that appeared in all forts 
of animals, birds, beafts, and fifties, upon the extinction 
of the Sun, fince ourfelves could not behold it without 
fome fenfe of horror.” 
Of the Limits and Periods of Solar and Lunar 
Eclipses. 
The diftance of the Moon in degrees'and minutes, above 
or below the ecliptic line, is called her latitude. If Ihu 
be above the ecliptic, flie has pafted her afeending node, 
and is faid to have north latitude ; if below it, (lie has 
pafted her defeendivg node, and is faid to have fouth lati¬ 
tude. If the latitude at any time exceed the fum of the 
femi-diameter of the Moon, equal to i6| minutes, and 
the Earth’s fhadow' equal to 45£ minutes, the Moon at 
that time cannot be eclipfed ; but will either pafs under 
or over the fhadow, according as flie happens to be above 
or below the ecliptic line. The diftance from the node, 
either before or after it, correfponding to the above ex¬ 
tent, is about twelve degrees, which is confequently the 
limit of lunar eclipfes : for, whena full Moon or oppofition 
happens within twelve degrees of the nodes, fhe will be 
eclipfed; and, the nearer to the nodes, the greater will the 
eclipfe be. 
If at the conjunction, or new Moon, the latitude of the 
Moon exceeds the fum of the femi-diameters of tlie Sun 
i6| minutes, and of the Moon i6§ minutes, we fhould 
fee no eclipfe of the Sun from the centre of the Earth. 
But as we view the luminaries from the furface, which is 
much higher, we are obliged to take in the femi-diameter 
of the Earth as feen from the Moon. Then, if the lati¬ 
tude of tlie Moon be greater than the fum of thefe three 
numbers, 94T minutes, the Sun will not be eclipfed ; for 
the Moon will pafs either over or under his di(k, according 
as (lie is above or below the ecliptic line. The diftance 
from the node on either fide agreeing to the above-men¬ 
tioned extent, is the eighteen degrees which is tlie utmoft 
limit of folar eclipfes; whence it follows, that if tlie Sun 
and Moon, at the time of a conjunction or new Moon, 
happen to be within eighteen degrees of the node, the Sun 
will be eclipfed. Now, if a conjunction happen at or very 
near the node, there will be a great folar eclipfe; but at 
the preceding oppofition, if the Earth was not got into 
the lunar ecliptic limits, at the next oppofition it will be 
got beyond it; hence at each node there may happen only 
one folar eclipfe, and therefore in a year there may happen 
only two folar eclipfes. Indeed there muft be one con¬ 
junction happen in the time in which the Earth is palling 
through the folar ecliptic limits, and confequently there 
muft be one folar eclipfe happen at each node; hence there 
muft: be two folar eclipfes at lead in a year. 
If an oppofition happen juft before the Earth gets into 
the lunar ecliptic limit, the next oppolition may not hap¬ 
pen till the Earth is got beyond the limit on the other fide 
of the node ; confequently there may not be a lunar eclipfe 
at the node; hence there may not be an eclipfe of the 
Moon in the courfe of a year. When therefore there are 
only two eclipfes in a year, they muft be both of tlie Sun. 
If there be an eclipfe of the Moon as foon as the Earth 
gets within the lunar ecliptic limit, it will be got out of 
the limit before the next oppofition ; confequently there 
can be only one lunar eclipfe at the fame node. But, as 
the lunar nodes move backwards about nineteen degrees in 
a year, tlie Earth may come within the lunar ecliptic limits, 
at the fame node, a fecond time in the courfe of a year, 
and therefore there may be three lunar eclipfes in a year; 
and there can be no more. 
If ail eclipfe of the Moon happen at or very near to the 
node, a conjunction may happen before and after, whilft 
the Earth is within the folar ecliptic limits; hence there 
may, at each node, happen two eclipfes of the Sun and 
one of the Moon ; and in this cafe, the eclipfes of the 
Sun will be fmall, and that of the Moon large. Thus 
when 
