Ragnarok : the age of fire and gravel

104 THE COMET.

And certainly the presence of ice could not decompose rocks a hundred feet deep, and change their chemical constitution. Nothing but heat could do it.

But we have seen that the comet is self-luminousthat is, it is in process of combustion; it emits great gushes and spouts of luminous gases ; its nucleus is enveloped in a cloak of gases. What effect would these gases have upon our atmosphere ?

First, they would be destructive to animal life. But it does not follow that they would cover the whole earth. If they did, all life must have ceased. They may have fallen in places here and there, in great sheets or patches, and have caused, until they burned themselves out, the conflagrations which the traditions tell us accompanied the great disaster.

Secondly, by adding increased proportions to some of the elements of our atmosphere they may have helped to produce the marked difference between the pre-glacial and our present climate.

What did these gases consist of ?

Here that great discovery, the spectroscope, comes to our aid. By it we are able to tell the elements that are being consumed in remote stars; by it we have learned that comets are in part self-luminous, and in part shine by the reflected light of the sun ; by it we are even able to identify the very gases that are ina state of combustion in comets.

In Schellen’s great work* I find a cut (see next page) comparing the spectra of carbon with the light emitted by two comets observed in 1868—Winnecke’s comet and Brorsen’s comet.

Here we see that the self-luminous parts of these com-

* “Spectrum Analysis,” p. 396.