is the philosopher, I shall, before closing this chapter, present some
paragraphs upon the subject from the pen of a professor of mathematics
and mechanics.

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