ㅤㅤThe brilliancy of the moon arises solely from the light of the sun, which falls on the dark or not self-luminous substance of the moon. Out of the vast flood of light, which the sun pours forth with such prodigality into space, the dark body of the moon intercepts a little, and of that little it reflects a small fraction to illuminate the earth. The moon sheds so much light, and seems so bright, that it is often difficult at night to remember that the moon has no light except what falls on it from the sun. Nevertheless, the actual surface of the brightest full moon is perhaps not much brighter than the streets of London on a clear sunshiny day. A very simple observation will suffice to show that the moon's light is only sunlight. Look some morning at the moon in daylight, and com- pare the moon with the clouds. The brightness of the moon and of the clouds are directly comparable, and then it is seen plainly that the sun which illuminates the clouds has also illumined the moon.