14.  THE “TELEPHONE EXCHANGE.”—­“We are accustomed to talk,” writes Professor Karl Pearson,[1] “of the ‘external world,’ of the ‘reality’ outside us.  We speak of individual objects having an existence independent of our own.  The store of past sense-impressions, our thoughts and memories, although most probably they have beside their psychical element a close correspondence with some physical change or impress in the brain, are yet spoken of as inside ourselves.  On the other hand, although if a sensory nerve be divided anywhere short of the brain, we lose the corresponding class of sense impression, we yet speak of many sense-impressions, such as form and texture, as existing outside ourselves.  How close then can we actually get to this supposed world outside ourselves?  Just as near but no nearer than the brain terminals of the sensory nerves.  We are like the clerk in the central telephone exchange who cannot get nearer to his customers than his end of the telephone wires.  We are indeed worse off than the clerk, for to carry out the analogy properly we must suppose him never to have been outside the telephone exchange, never to have seen a customer or any one like a customer—­in short, never, except through the telephone wire, to have come in contact with the outside universe.  Of that ‘real’ universe outside himself he would be able to form no direct impression; the real universe for him would be the aggregate of his constructs from the messages which were caused by the telephone wires in his office.  About those messages and the ideas raised in his mind by them he might reason and draw his inferences; and his conclusions would be correct—­for what?  For the world of telephonic messages, for the type of messages that go through the telephone.  Something definite and valuable he might know with regard to the spheres of action and of thought of his telephonic subscribers, but outside those spheres he could have no experience.  Pent up in his office he could never have seen or touched even a telephonic subscriber in himself.  Very much in the position of such a telephone clerk is the conscious ego of each one of us seated at the brain terminals of the sensory nerves.  Not a step nearer than those terminals can the ego get to the ’outer world,’ and what in and for themselves are the subscribers to its nerve exchange it has no means of ascertaining.  Messages in the form of sense-impressions come flowing in from that ‘outside world,’ and these we analyze, classify, store up, and reason about.  But of the nature of ‘things-in-themselves,’ of what may exist at the other end of our system of telephone wires, we know nothing at all.