342. The nearer that the Penumbra’s center is to the Equator at the middle of the general Eclipse, the longer is the duration of the Eclipse at all those places where it is central; because, the nearer that any place is to the Equator, the greater is the Circle it describes by the Earth’s motion on its Axis: and so, the place moving quicker keeps longer in the Penumbra whose motion is the same way with that of the place, tho’ faster as has been already mentioned § 337. Thus, (see the Earth at _D_ and the Penumbra at _12_) whilst the point _b_ in the polar Circle _abcd_ is carried from _b_ to _c_ by the Earth’s diurnal motion, the point _d_ on the Tropick of Cancer _T_ is carried a much greater length from _d_ to _D_: and therefore, if the Penumbra’s center goes one time over _c_ and another time over _D_, the Penumbra will be longer in passing over the moving place _d_ than it was in passing over the moving place _b_. Consequently, central Eclipses about the Poles are of the shortest duration; and about the Equator of the longest. [Sidenote: And shortens the duration of some which fall within these Circles.] 343. In the middle of Summer the whole frigid Zone included by the polar Circle _abcd_ is enlightened; and if it then happens that the Penumbra’s center goes over the north Pole, the Sun will be eclipsed much the same number of Digits at _a_ as at _c_; but whilst the Penumbra moves eastward over _c_ it moves westward over _a_, because with respect to the Penumbra, the motions of _a_ and _c_ are contrary: for _c_ moves the same way with the Penumbra towards _d_, but _a_ moves the contrary way towards _b_; and therefore the Eclipse will be of longer duration at _c_ than at _a_. At _a_ the Eclipse begins on the Sun’s eastern limb, but at _c_ on his western: at all places lying without the polar Circles, the Sun’s Eclipses begin on his western limb, or near it, and end on or near his eastern. At those places where the Penumbra touches the Earth, the Eclipse begins with the rising Sun, on the top of his western or uppermost edge; and at those places where the Penumbra leaves the Earth, the Eclipse ends with the setting Sun, on the top of his eastern edge which is then the uppermost, just at its disappearing in the Horizon. [Sidenote: The Moon has no Atmosphere.] 344. If the Moon were surrounded by an Atmosphere of any considerable Density, it would seem to touch the Sun a little before the Moon made her appulse to his edge, and we should see a little faintness on that edge before it were eclipsed by the Moon: But as no such faintness has been observed, at least so far as I ever heard, it seems plain, that the Moon has no such Atmosphere as that of the Earth. The faint ring of light surrounding the Sun in total Eclipses, called by CASSINI _la Chevelure du Soleil_, seems to be the Atmosphere of the Sun; because it has been observed to move equally with the Sun, not with the Moon. [Sidenote: PLATE XI.]