Why is this, in some degree, necessary?
[§ 25.] Is the Sun himself also known to turn on its axis like the Planets? How many days does he need for one complete rotation? By what means have we been able to observe this motion?
[§ 26.] Have the Moon and the Satellites of the other Planets also a rotary motion? In what position does the Moon remain with regard to the Earth? But what is her monthly revolution round the Earth equal to? Why? What is a day in the Moon equal to? Why?
FOOTNOTES:
[4] The propriety of this comparison becomes still more evident, when we reflect that the Axis of the top is generally somewhat inclined to the plane.
[5] If the terms perpendicular and oblique, should not be perfectly understood by the pupils, it will be easy for the teacher to explain their meaning.
[6] If the Earth requires 365 days to travel round the Sun; and each day has twentyfour hours; then the Earth will, during the whole of this time, turn Three Hundred and Sixtyfive times on its axis.
LESSON V.
OF THE APPEARANCE AND PECULIARITIES OF THE MOON AND SOME OF THE PLANETS WHEN VIEWED THROUGH A TELESCOPE.
§ 27. Next to the Sun there is no heavenly body so interesting to us as the Moon. When viewed through a good Telescope[7] she has nearly the same appearance as in Figure I, Plate [X]. The bright parts are supposed to be lofty mountains and tracts of land; (which is evident also from the shadow which they cast) and the dark spots are supposed to be valleys and caverns. Many of the mountains of the Moon are higher than the largest mountains on the Earth. Some of them are volcanos, and their eruptions have been distinctly observed by many distinguished Philosophers. Some of the caverns are ascertained to have a depth of many miles and a width of almost Three miles.—No water has as yet been discovered in the Moon. Hence if she is inhabited, as we have reason to believe, her inhabitants must be very differently constructed from ourselves.