Page:Popular Science Monthly Volume 20.djvu/316

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lar books were kept by them for recording observations. They kept account of the phases and the corresponding relative positions of the sun, moon, and earth. This led to a very interesting discussion as to what makes the moon shine. In the course of this, they drew diagrams and experimented with the ball and light. They detected the earth-shine, and settled its cause for themselves; found out that the moon moves round the earth, and noted the time; noted the hours of rising; noted the various constellations through which the moon takes its path; and noted the effect of their situation on the moon's time of rising. After these points had been settled, I asked them, had they ever seen the moon show more than one face. As this called attention to the fact that the moon always shows (substantially) the same face, the cause was discussed. To settle it, a girl stood in the middle of the room and another walked round, facing her all the time. They finally settled for themselves that the moon revolves once on its axis while it moves once round the earth. I gave them no further help than the question I have just stated. I have not yet had pupils trace the moon's path and that of the sun so accurately as to discover the nodes, but I certainly shall try to do so, and to have the retrograde motion of the nodes detected; the time (approximate) of their revolution. I shall pass over nothing that ordinary eyes can see, ordinary minds reason out.

The study of planets affords delightful work. Some of my pupils have studied Mercury with great interest, finding that his orbit is within that of the earth and of Venus; finding the direction of his motion round the sun, and the period. The study of Mars is in the highest degree profitable, and so is that of Venus. The young folks can readily discover the retrograde motions, and, with the simple suggestion that the apparent retrograde may result from the changed position from which we view the planet, may find the relative positions and detect the cause.

I occasionally report to my young astronomers a little of the testimony of other persons. Thus, in discussing the cause of the moon's light, I told them of stars occulted by the dark part of the moon. In doing so, I always wait until they have exhausted the evidence of their own senses; and I am specially careful to distinguish between the two kinds of testimony. It leads, with older girls, into some very interesting discussions as to the value of other people's evidence.

Sometimes some of the girls begin to guess. I always take special care (in a good-natured way) that guessers shall come to shame. I endeavor to make them as accurate as possible, allowing the evidence to prove just what it ought, and no more.

My pupils have been so much interested in astronomy, that their talk about it has brought to me a good many persons who wish to sell me some sort of apparatus for illustrating the motions of the solar system or some part of it. I do not much believe in these contriv-