Countless instances can be cited of the persistence of men, even in civilized lands, in following a certain practice for long periods, until someone possessing the inventive faculty has devised a better one. For the sake of brevity, only two cases, and those well known, will be mentioned as illustrative. One was the invention of movable type, and the other that of pointing the wood screw. Man had continued for centuries to make blocks of wood or other material on which words and phrases were engraved or cut, and then to print from them. Suddenly a man in Germany (usually said to be John Guttenberg) made the change, so slight in appearance and yet so tremendous in results, of cutting only one letter on a block, and arranging and securing the blocks in such a way as to enable him to print any word or words desired. This did not occur until about the year 1434 A. D. Why had not someone done this in all the long centuries? Surely it was not because men of great reasoning faculties had not lived; for in the long interval the civilization of Egypt, Assyria, Babylon, Persia, Greece and Rome had flourished; and Plato, Aristotle, Cæsar and the great inventor Archimedes had lived! Similarly, men continued to use in wood the same flat pointed screw that they used in metals, boring the hole first in the wood with a gimlet, and then entering the flat point of the screw into the hole. Suddenly (but not until the nineteenth century A. D.) an inventor made and patented a screw which came to a sharp point like a gimlet, which could be forced into wood just as the gimlet was, and then screwed into the wood without further ado. How can we explain the curious fact that countless men of reason, intelligence and mechanical skill had continued century after century to bore into wood with gimlets, and then follow the gimlet with flat-pointed screws? The explanation seems to be expressed in the phrase, "the idea had not occurred to them." Why had it not occurred to them? This question cannot, of course, be answered convincingly; but it may be pointed out that there is a small class of men to whom original ideas seem to come of their own accord. The inventor of mechanical appliances is in this class, and is perhaps its most conspicuous exemplar. * * * * * It may be pointed out, however, that the inventors of mechanical appliances are not the only men to whom original conceptions come; for original conceptions evidently come to the poets, the novelists, the musical composers, the artists, the strategists, the explorers, the statesmen, the philosophers, the founders of religions and the initiators of all enterprises great and small. It may be pointed out also that their mental processes are similar, and that they are best described by the greatest of all poets in the lines--