392 OF THE ECLIPSES OF THE

and takes place upon those parts of the earthwhich are only partially deprived of the fun’srays. For let S be the fun, E the earth, and m themoon; then if two right lines be drawn fromA and B to touch the body of the moon in rri. xviii. and s, they will form the cone r o s, which is thefigure of her dark shadow, as it falls upon theearth at o ; and two other lines, drawn throughthe fame points transversely, will shew the limitsof the penumbra, or faint shadow CriD; inevery part of which space there is more or lesslight, according as it is farther from, or nearerto the center o.

And as the moon moves eastward over thefun’s disc, the dark stiadow describes the pathC D, and all the inhabitants, living within thattract, will have the fun successively and totallyeclipsed ; whilst those who are at some distancefrom it, will have a partial eclipse, according asthey are more or less within the circle of thepenumbra C r s D. So that when the penum-bra first touches the earth, the general eclipse be-gins, and when it leaves the earth the eclipseends; the whole duration, at a mean rate, beingabout five hours and fifty minutes.pi. xviii. The earth’s dark shadow F C D G, is also en-2 ‘ compassed by a penumbra, in the same manneras the moon’s, which is faint towards the edgesC r and D s, and more obscure towards C F andD G; and this is the reason why it is so difficult

to