7. _It is by light reflected from opake bodies that most of the objects around us are rendered visible._ When a lighted candle is brought into a dark room, not only the candle but all other bodies in the room become visible. Rays of the sun passing into a dark room render luminous a sheet of paper on which they fall, and this sheet in its turn enlightens, to a certain extent, the whole apartment, and renders objects in it visible, so long as it receives the rays of the sun. In like manner, the moon and the planets are opake bodies, but the light of the sun falling upon them, and being reflected from their surfaces, renders them visible. Were no light to fall on them from the sun, or were they not endued with a power of reflecting it, they would be altogether invisible to our sight. When the moon comes between us and the sun, as in a total eclipse of that luminary, as no solar light is reflected from the surface next the earth, she is invisible--only the curve or outline of her figure being distinguished by her shadow. In this case, however, there is a certain portion of reflected light on the lunar hemisphere next the earth, though not distinguishable during a solar eclipse. The earth is enlightened by the sun, and a portion of the rays which fall upon it is reflected upon the dark hemisphere of the moon which is then towards the earth. This reflected light from the earth is distinctly perceptible, when the moon appears as a slender crescent, two or three days after new moon--when the earth reflects its light back on the moon, in the same manner as the full moon reflects her light on the earth. Hence, even at this period of the moon, her whole face becomes visible to us, but its light is not uniform or of equal intensity. The thin crescent on which the full blaze of the solar light falls, is very brilliant and distinctly seen, while the other part, on which falls only a comparatively feeble light from the earth, appears very faint, and is little more than visible to the naked eye, but with a telescope of moderate power,--if the atmosphere be very clear--it appears beautifully distinct, so that the relative positions of many of the lunar spots may be distinguished.