burning glasses have been constructed with which iron, steel, and even flints have been actually melted by the sun's heat. It can be proved that the sun himself must be hotter than any temperature that can be produced in the focus of the most powerful burning glass. We certainly cannot conceive any organized being which would find a congenial residence in a temperature vastly hotter than that of the most powerful furnace that has ever been known. Assuredly there can be no life on the sun.
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Fig. 6.—The Clouds on Jupiter, October 14th, 1891.
The next celestial world in importance to the sun is, of course, the moon. Could we find here an eligible abode for mankind? The moon would, no doubt, provide the necessary alternation from day to night, but the day on
