earth: this is called an eclipfe of the fun; it may be either partial or total.

An eclipfe of any lucid body, is a deficiency or diminution of light, which would otherwife come from it to our eye, and is caufed by the interpofition of fome opake body.

The eclipfes of the fun and moon, though expreffed by the fame word, are in nature very different; the fun, in reality, lofes nothing of it's native luftre in the greatest eclipfes, but is all the while inceffantly fending forth ftreams of light every way round him, as copiously as before, Some of these streams are, however, intercepted in their way towards our earth, by the moon coming between the earth and the fun: and the moon having no light of her own, and receiv ing none from the fun on that half of the globe which is towards our eye, muft appear dark, and make fo much of the fun's difk appear fo, as is hid from us by her interpofition."

What is called an eclipfe of the fun, is therefore, in reality, an eclipfe of the earth, which is deprived of the fun's light, by the moon's coming between, and cafting a fhadow upon it. The earth being a globe, only that half of it which at any time is turned towards the fun, can be enfightened by him at that time; it is upon fome part of this enlightened half of the earth, that the moon's fhadow, or penumbra, falls in a folar eclipfe.

The fun 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 fun; or in other words, the fun will not be eclipfed, unless the moon at that time is in or near one of her podes.

The moon, howeyer, cannot be directly be

tween

tween the fun and us, unless they are both in the fame part of the heavens; that is, unlefs they are in conjunction. Therefore, the fun can never be eclipfed but at the new moon, nor even then, unless the moon at that time is in or near one of her nodes.

The moon being much fmaller than the earth, and having a conical fhadow, because fhe is lefs than the fun, can only cover a fmall part of the earth by her fhadow; 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 fun is vifible but to a few inhabitants of the earth; whereas an eclipfe of the moon may be seen by all thofe that are on that hemifphere which is turned towards it. In other words, as the moon can never totally eclipfe the earth, there will be many parts of the globe that will fuffer no eclipfe, though the fun be above their horizon.

An eclipfe of the fun always begins on the western, and ends on the eaflern fide; because the moon moving in her orbit from weft to east, neceffarily first arrives at and touches the fun's western limb, and goes off at the eaftern.

It is not neceffary, in order to conftitute a central eclipfe of the fun, that the moon should be exactly in the line of the nodes, at the time of it's conjunction; for it is fufficient to denominate an eclipfe of the fun central, that the center of the moon be directly between the center of the fun, and the eye of the fpectator; for to him, the fun is then centrally eclipfed. But as the fhadow 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 fun may be eclipfed centrally, totally, partially, and not at all, at the fame time.

total

A total eclipfe of the fun is a very curious fpectacle: Clavius fays that, in that which he obferved in Portugal, in 1650, the obfcurity was greater, or more fenfible than that of the night: the largest ftars made their appearance for about a minute or two, and the birds were fo terrified, that they fell to the ground.

Thus in fig. 3, pl. 10, let A B C be the fun, M N the moon, h 1 g part of the cone of the moon's fhadow; f d the penumbra of the moon: from this figure it is easy to perceive,

1. That thofe parts of the earth that are within the circle reprefented by g h, are covered by the fhadow of the moon, fo that no rays can come from any part of the fun 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 fun is vifible; thus between d and g, the parts of the fun near C cannot be feeh, the rays coming from thence towards d or g, being intercepted by the moon: whereas at the fame time, the parts between f and h are illuminated by rays coming from C, but are deprived by the moon of fuch as come from A.

3. The nearer any part of the earth, within the penumbra, is to the fhadow of the moon, as in places near g, 1, or h, the lefs is the portion of the fun vifible to it's inhabitants; the nearer it is to the outfide of the penumbra, as towards d, e, or f, the greater is the portion feen.

4. Out of the penumbra the entire difk is vifible.

The quantity of a folar eclipfe in general is according to the fize of the moon's fhade projected upon the earth; this fhade is largest when the earth is in aphelion, the moon in perigee.

The quantity of a folar eclipfe to those within the line which the center of the moon's fhade defcribes

tween the fun and us, unless they are both in the fame part of the heavens; that is, unless they are in conjunction. Therefore, the fun can never be eclipfed but at the new moon, nor even then, unless the moon at that time is in or near one of her nodes.

The moon being much fmaller than the earth, and having a conical fhadow, becaufe fhe is lefs than the fun, can only cover a fmall part of the earth by her shadow; 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 fun is visible but to a few inhabitants of the earth; whereas an eclipse 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 totally eclipfe the earth, there will be many parts of the globe that will fuffer no eclipfe, though the fun be above their horizon.

An eclipfe of the fun always begins on the weftern, and ends on the eaflern fide; because the moon moving in her orbit from weft to cast, neceffarily first arrives at and touches the fun's western limb, and goes off at the eastern.

It is not neceffary, in order to conftitute a central eclipfe of the fun, that the moon fhould be exactly in the line of the nodes, at the time of it's conjunction; for it is fufficient to denominate an eclipfe of the fun central, that the center of the moon be directly between the center of the fun, and the eye of the fpectator; for to him, the fun is then centrally eclipfed. But as the fhadow of the moon can cover but a fimall portion of the earth, it is obvious this may happen when the moon is not in one of her nodes. Further, the fun may be eclipfed centrally, totally, partially, and not at all, at the fame time.

A total

A total eclipfe of the fun is a very curious. fpectacle: Clavius fays that, in that which he obferved in Portugal, in 1650, the obscurity was greater, or more fenfible than that of the night: the largest ftars made their appearance for about a minute or two, and the birds were fo terrified, that they fell to the ground.

Thus in fig. 3, pl. 10, let A B C be the fun, MN the moon, h 1 g part of the cone of the moon's fhadow; f d the penumbra of the moon: from this figure it is eafy to perceive,

1. That those parts of the earth that are within the circle reprefented by g h, are covered by the fhadow of the moon, fo that no rays can come from any part of the fun into that circle, on account of the interpofition of the moon.

2. In those parts of the earth where the penumbra falls, only part of the fun is vifible; thus between d and g, the parts of the fun 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 h are illuminated by rays coming from C, but are deprived by the moon of fuch as come from A.

3. The nearer any part of the earth, within the penumbra, is to the fhadow of the moon, as in places near g, 1, or h, the lefs is the portion of the fun vifible to it's inhabitants; the nearer it is to the outfide of the penumbra, as towards d, e, or f, the greater is the portion seen.

4. Out of the penumbra the entire difk is vifible.

The quantity of a folar eclipfe in general is according to the fize of the moon's fhade projected upon the earth; this fhade is largeft when the earth is in aphelion, the moon in perigee.

The quantity of a folar eclipfe to those within the line which the center of the moon's fhade defcribes