In the ages to come man may be able to predict, perhaps even to control, the wayward courses of the winds and the clouds, but hardly will his puny hands have strength to speed afresh our slackening planet in its orbit or rekindle the dying fire of the sun. Yet the philosopher who trembles at the idea of such distant catastrophes may console himself by reflecting that these gloomy apprehensions, like the earth and the sun themselves, are only parts of that unsubstantial world which thought has conjured up out of the void, and that the phantoms which the subtle enchantress has evoked to-day she may ban to-morrow. They too, like so much that to the common eye seems solid, may melt into air, into thin air.