337. By Fig. II it is plain, that the Sun is totally or centrally eclipsed but to a small part of the Earth at any time; because the dark conical shadow _e_ of the Moon _M_ falls but on a small part of the Earth: and that the partial Eclipse is confined at that time to the space included by the Circle _a 0 b_, of which only one half can be projected in the Figure, the other half being supposed to be hid by the convexity of the Earth _E_: and likewise, that no part of the Sun is eclipsed to the large space _YY_ of the Earth, because the Moon is not between the Sun and that part of the Earth: and therefore to all that part the Eclipse is invisible. The Earth turns eastward on its Axis, as from _g_ to _h_, which is the same way that the Moon’s shadow moves; but the Moon’s motion is much swifter in her Orbit from _s_ to _t_: and therefore, altho’ Eclipses of the Sun are of longer duration on account of the Earth’s motion on its Axis, than they would be if that motion was stopt, yet in 3 minutes and 13 seconds of time, the Moon’s swifter motion carries her dark shadow quite over any place that its center touches at the time of greatest obscuration. The motion of the shadow on the Earth’s Disc is equal to the Moon’s motion from the Sun, which is about 30-1/2 minutes of a degree every hour at a mean rate; but so much of the Moon’s Orbit is equal to 30-1/2 degrees of a great Circle on the Earth, § 320; and therefore the Moon’s shadow goes 30-1/2 degrees or 1830 geographical miles on the Earth in an hour, or 30-1/2 miles in a minute, which is almost four times as swift as the motion of a cannon-ball. [Sidenote: PLATE XI. Fig. IV. Phenomena of the Earth as seen from the Sun or New Moon at different times of the year.]