IT has been shown that the moon is not a reflector of the sun's light, but is self-luminous. That the luminosity is confined to one-half its surface is sufficiently shown by the fact that at "new moon" the entire circle or outline of the whole moon is often distinctly visible, but the darker. outline or circle is always apparently less than the segment which is illuminated. It is a well ascertained fact that a luminous body appears larger, or subtends a greater angle at the eye, than a body of exactly the same magnitude, but which is not luminous. Hence, it is logically fair to conclude that as the part of the moon which is non-luminous is always of less magnitude than the part which is luminous, that luminosity is attached to a part only. From this fact it is easily understood that "new moon," "full moon," and "gibbous moon," are simply the different proportions of the illuminated surface which are presented to the observer on earth. A very simple experiment will both illustrate and imitate these different phases. Take
a wooden or other ball, and rub one half its surface with a solution of phosphorus in olive oil. On slowly turning this round in a dark room, all the quarters and intermediate phases of the moon will be most beautifully represented.