336. To make the last five articles and several other Phenomena plainer, let _S_ be the Sun, _E_ the Earth, _M_ the Moon, and _AMP_ the Moon’s Orbit. Draw the right line _Wc 12_ from the western edge of the Sun at _W_, touching the western edge of the Moon at _c_ and the Earth at _12_: draw also the right line _Vd 12_ from the eastern edge of the Sun at _V_, touching the eastern edge of the Moon at _d_ and the Earth at _12_: the dark space _ce 12 d_ included between those lines is the Moon’s shadow, ending in a point at _12_ where it touches the Earth; because in this case the Moon is supposed to change at _M_ in the middle between _A_ the Apogee, or farthest point of her Orbit from the Earth, and _P_ the Perigee, or nearest point to it. For, had the point _P_ been at _M_, the Moon had been nearer the Earth; and her dark shadow at _e_ would have covered a space upon it about 180 miles broad, and the Sun would have been totally darkened as at _A_ (Fig I) with some continuance: but had the point _A_ (Fig. II) been at _M_, the Moon would have been farther from the Earth, and her shadow would have ended in a point about _e_, and therefore the Sun would have appeared as at _B_ (Fig. I) like a luminous ring all around the Moon. Draw the right lines _WXdh_ and _VXcg_, touching the contrary sides of the Sun and Moon, and ending on the Earth at _a_ and _b_: draw also the right line _SXM 12_, from the center of the Sun’s Disc, through the Moon’s center, to the Earth at _12_; and suppose the two former lines _WXdh_ and _VXcg_ to revolve on the line _SXM 12_ as an Axis, and their points _a_ and _b_ will describe the limits of the Penumbra _TT_ on the Earth’s surface, including the large space _a0b12a_; within which the Sun appears more or less eclipsed as the places are more or less distant from the verge of the Penumbra _a0b_. [Sidenote: Digits, what.] Draw the right line _y 12_ across the Sun’s Disc, and parallel to the plane of the Moon’s Orbit; divide this line into twelve equal parts, as in the Figure, for the twelve [76]Digits of the Sun’s diameter: and at equal distances from the center of the Penumbra _TT_ to its edge on the Earth, or from _12_ to _0_, draw twelve concentric Circles, as marked with the numeral Figures _1_ _2_ _3_ _4_ &c. and remember that the Moon’s motion in her Orbit _AMP_ is from west to east, as from _s_ to _t_. Then, [Sidenote: The different phases of a solar Eclipse. PLATE XI. Fig. III.]