APPENDIX. 



SUPPLEMENTARY NOTES. 



A. Page 41. — The surface of the moon. — The moon is the only 

 planetary body placed sufficiently near us, to have the inequalities of 

 its surface rendered distinctly visible with the telescope. Attendant 

 on the earth, and having nearly the same density, we may reasonably 

 infer that the mineral substances of which it is composed do not differ 

 essentially from those on the surface of our own planet. If, as is most 

 probable, the moon is surrounded by an atmosphere, it must be very 

 clear and low, for it scarcely occasions a sensible refraction of the rays 

 of light when it passes over the fixed stars. Many of the dark parts 

 of the moon, particularly the part called mare crisium, appear to be 

 covered with a fluid, which is probably more transparent than water, 

 as the forms of the rocks and craters are seen beneath it, but not so 

 distinctly as in the lighter parts of the moon's surface. To examine 

 the moon with a reference to its external structure, the defining power 

 of the telescope should be of the first quality, sufficient to show the 

 projections of the outer illuminated limb, as distinctly as they appear 

 when the moon is passing over the disk of the sun during a solar 

 eclipse. With such a telescope, and a sufficient degree of light and of 

 magnifying power, almost every part of the moon's surface appears to 

 be volcanic, containing craters of enormous magnitude and vast depth : 

 the shelving rocks, and the different internal ridges within them, 

 seem to mark the stations at which the lava has stood and formed a 

 floor during different eruptions ; while the cones in some of the 

 craters resemble those formed within modern volcanoes. The largest 

 mountain on the southern limb of the moon, like the largest volcanic 

 cone on the earth, Chimborazo, has no deep crater on its summit. 

 There are indeed the outlines of the crater, but it is nearly filled 

 G G2 



