Other writers, however, try to reach Mr. Kidd's conclusion by a somewhat different route. Whether the great man is or is not a more common phenomenon than he seems to be, they maintain that his conquests in the realms of invention and discovery, when once made, really "become common property," of which all men could take advantage if it were not for artificial monopolies. All men, therefore, though not equal as discoverers, are practically equalised by whatever the discoverers accomplish. Now, of the simpler inventions and discoveries, such as that of fire for example, this is perfectly true; but it is true of these only. As inventions and discoveries grow more and more complex, they no more become common property, as soon as certain men have made them, than encyclopaedic knowledge becomes the property of every one who buys or happens to inherit an edition of the _Encyclopaedia Britannica_. It is perfectly true that the discovery of each new portion of knowledge enables men to acquire it who might never have acquired it otherwise; but as the acquisition of the details of knowledge becomes facilitated, the number of details to be acquired increases at the same time; and the increased ease of acquiring each is accompanied by an increased difficulty in assimilating even those which are connected most closely with each other. We may safely say that a knowledge of the simple rules of arithmetic is common to all the members of the English University of Cambridge; but out of some thousands of students only a few become great mathematicians. And the same thing holds good of scientific knowledge in general, and especially of such knowledge as applied to the purposes of practical industry. Knowledge and inventions, once made, are like a river which flows by everybody; but the water of the river becomes the property of individuals only in proportion to the quantity of it which their brains can, as it were, dip up; and the knowledge dipped up by the small brains is no more equal to that dipped up by the large than a tumbler of water is made equal to a hogshead by the fact that both vessels have been filled from the same stream.