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6 that extra-terrestrial life means extra-terrestrial human life. Such an inference recalls to my mind the exclamation of an innocent globetrotter to a friend of mine in Japan once, a connoisseur of Japanese painting, upon being told that the Japanese pictures were exceedingly fine. "What!" the globe-trotter exclaimed in surprise, "do the Japanese have pictures,—real pictures, I mean, in gilt frames?" The existence of extra-terrestrial life does not involve "real life in trousers," or any other particular form of it with which we are locally conversant. Under changed conditions, life itself must take on other forms.

The next point is as to what constitutes proof. Now, between the truths we take for granted because of their age, and those we question because of their youth, we are apt to forget that in both proof is nothing but preponderance of probability. The law of gravitation, for example, than which we believe nothing to be more true, depends eventually, as recognized by us, upon a question of probability; and so do the thousand and one problems of daily life upon so many of which we act unhesitatingly and should be philosophic fools if we did not. All deduction rests ultimately upon the data derived from experience. This is the tortoise that supports our conception of the cosmos. For us, therefore, the point at issue in any