Then the earth is ever radiating away heat into space, the Professor reminds us.  And so at last comes a vision of earthly cherubim, hopping heads, great unemotional intelligences, and little hearts, fighting together perforce and fiercely against the cold that grips them tighter and tighter.  For the world is cooling—­slowly and inevitably it grows colder as the years roll by.  “We must imagine these creatures,” says the Professor, “in galleries and laboratories deep down in the bowels of the earth.  The whole world will be snow-covered and piled with ice; all animals, all vegetation vanished, except this last branch of the tree of life.  The last men have gone even deeper, following the diminishing heat of the planet, and vast metallic shafts and ventilators make way for the air they need.”

So with a glimpse of these human tadpoles, in their deep close gallery, with their boring machinery ringing away, and artificial lights glaring and casting black shadows, the Professor’s horoscope concludes.  Humanity in dismal retreat before the cold, changed beyond recognition.  Yet the Professor is reasonable enough, his facts are current science, his methods orderly.  The contemplative man shivers at the prospect, starts up to poke the fire, and the whole of this remarkable book that is not written vanishes straightway in the smoke of his pipe.  This is the great advantage of this unwritten literature:  there is no bother in changing the books.  The contemplative man consoles himself for the destiny of the species with the lost portion of Kubla Khan.

THE EXTINCTION OF MAN

It is part of the excessive egotism of the human animal that the bare idea of its extinction seems incredible to it.  “A world without us!” it says, as a heady young Cephalaspis might have said it in the old Silurian sea.  But since the Cephalaspis and the Coccosteus many a fine animal has increased and multiplied upon the earth, lorded it over land or sea without a rival, and passed at last into the night.  Surely it is not so unreasonable to ask why man should be an exception to the rule.  From the scientific standpoint at least any reason for such exception is hard to find.

No doubt man is undisputed master at the present time—­at least of most of the land surface; but so it has been before with other animals.  Let us consider what light geology has to throw upon this.  The great land and sea reptiles of the Mesozoic period, for instance, seem to have been as secure as humanity is now in their pre-eminence.  But they passed away and left no descendants when the new orders of the mammals emerged from their obscurity.  So, too, the huge Titanotheria of the American continent, and all the powerful mammals of Pleistocene South America, the sabre-toothed lion, for instance, and the Machrauchenia suddenly came to a finish when they were still almost at the zenith of their rule. And in no case does