40 OF THE SOLAR SYSTEM, AND THE

revolving round it continually, by a differentmotion, in the space of a month. The Moon’sdiameter is two thousand one hundred andeighty miles ; her distance from the Earth twohundred and forty thousand miles ; and in bulkshe is about sixty times less than the Earth. Jupiterhas four such Moons, and Saturn five; andfrom the continual change of their phases, orappearances, it is evident that these also areopaque bodies, like the planets, and shine onlyby means of the borrowed light which theyreceive from the Sun.

It may also be observed, that our earth is amoon to the moon, waxing and waneing in ex-actly the fame manner j but appearing aboutthirteen times larger, and, of course, affordinga proportional quantity of light. When shechanges to us, the earth will appear full to her,and when she is in her first quarter to us, theearth will be in her third quarter to her. And,as her axis is almost perpendicular to the planeof the ecliptic, one half of her orb will be con-stantly illuminated by the reflected light af-forded by the earth in the fun’s absence, whilstthe other half will have a fortnight’s darkness,and a fortnight’s light, alternately.

The rotation of the moon upon her axis, isalso performed in exactly the fame time thatshe goes once round the earth, as is evidentfrom her always presenting the same face to us

during