"How if Space is really full of things we cannot see and as yet do not know? How if all animals and some savages have a cell in their brain or a nerve which responds to the invisible world? How if all Space be full of these landmarks, not material in our sense, but quite real? A dog barks at nothing, a wild beast makes an aimless circuit. Why? Perhaps because Space is made up of corridors and alleys, ways to travel and things to shun? For all we know, to a greater intelligence than ours the top of Mont Blanc may be as crowded as Piccadilly Circus."