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150 decomposition belong only to sources of exceedingly high temperature, such as the sun.

206. We may, therefore, take it for granted that a perpetual light, like a perpetual motion, is an impossibility; and we have then to inquire if the same argument applies to our sun, or if an exception is to be made in his favour. Does the sun stand upon a footing of his own, or is it merely a question of time with him, as with all other instances of high temperature heat? Before attempting to answer this question let us inquire into the probable origin of the sun's heat.

207. Now, some might be disposed to cut the Gordian knot of such an inquiry by asserting that our luminary was at first created hot; yet the scientific mind finds itself disinclined to repose upon such an assertion. We pick up a round pebble from the beach, and at once acknowledge there has been some physical cause for the shape into which it has been worn. And so with regard to the heat of the sun, we must ask ourselves if there be not some cause not wholly imaginary, but one which we know, or at least suspect, to be perhaps still in operation, which can account for the heat of the sun.

Now, here it is more easy to show what cannot