“I readily believe that there are more invisible than visible Natures in the universe. But who will explain for us the family of all these beings, and the ranks and relations and distinguishing features and functions of each? What do they do? What places do they inhabit? The human mind has always sought the knowledge of these things, but never attained it. Meanwhile I do not deny that it is helpful sometimes to contemplate in the mind, as on a tablet, the image of a greater and better world, lest the intellect, habituated to the petty things of daily life, narrow itself and sink wholly into trivial thoughts. But at the same time we must be watchful for the truth and keep a sense of proportion, so that we may distinguish the certain from the uncertain, day from night.”