and richest intercourse with natural facts of any sort, and still more, of course, for those who are forced to get too much of their learning through less direct channels, the external world that we all believe in, the world of business and of sport, the world of duty and of delight, the world of the stars and of the solar system, of the molecules and of the protoplasm, the world of history and of geology, the world of art and of faith,—is in great measure to be defined, from our own private point of view, as "the world that the people tell about." I repeat, only to the very smallest degree are any of us able to verify, in our own persons, the existence and the nature of the Reality in which we all believe. The keenest observer, the most patient student of facts, comes in contact with but an infinitesimal portion of the external natural facts in whose existence, upon social grounds, he comes to be assured. What a small portion of the world of modern chemistry or of biology can the individual investigator, devoted collector of facts though he be, verify in his own private experience in the laboratory! For the most industrious specialist the field of his own specialty thus abounds in truths that he regards as already known, and that, since his science has once for all ascertained them, he is personally not called upon, unless incidentally, to reëstablish by private research. If already within one's own field of work this dependence of the individual upon the work and the reports of his fellows is so extended, what shall be said of the unexplored oceans of truth that lie for each man beyond the shores of his own domain,—oceans of whose lands and wonders he hears frequent, if fragmentary, reports from other men. Yet, in just these oceans of truth lies the universe, the external world, as each man conceives it, so soon as he thinks of what belongs beyond his personal range. Your belief in the existence, at the present or in past time, of Africa, of the North Pole, of Julius Caesar, of the law of gravitation, of the current prices of given railway shares, of the molecules that compose a gas, or of the latest affair of gossip in European politics;—all such beliefs, I say, will illustrate to how vast an extent your actual external world is even now, not the world
