The situation is the same, in whatever field genius finds expression. Napoleon, by many considered the greatest military genius in the history of mankind, believed from his own experience that the fate of battles usually turned not so much on conscious planning and manœuvring as on tactics dictated by “latent thoughts” arising suddenly in the mind. “The decisive moment approached; the spark burst forth, and one was victorious.” In like manner there frequently has come to scientists and inventors, with the unexpectedness of lightning out of a clear sky, the discovery of natural laws or mechanical principles of which they previously had no conscious knowledge whatever. Everybody has heard the story of Newton, the falling apple, and the discovery of the law of gravitation; and of Galileo’s invention of the pendulum, born of the thoughts springing up in his mind while idly watching the oscillations of the great bronze lamp swinging from the roof of Pisa Cathedral. Not so well known, but particularly impressive because of its revelation of the manner in which the desultory development of a train of thought in the mind of a man of genius may lead to a subconscious upsurging of the highest value, is Alfred Russel Wallace’s own account of his epoch-making discovery of the scientific doctrine of the origin of species—a discovery achieved by him, in the far-off Malay Archipelago, with no knowledge that the same doctrine had even then been worked out, though not as yet made public, by Charles Darwin. “At the time in question,” Wallace relates, in his “My Life,” “I was suffering from a sharp attack of intermittent fever, and every day during the cold and succeeding hot fits had to lie down for several hours, during which time I had nothing to do but to think over any subjects then particularly interesting me. One day something brought to my mind Malthus’s ‘Principle of Population,’ which I had read about twelve years before. I thought of his clear exposition of the ‘positive checks to increase’—disease, accidents, war, and famine—which keep down the population of savage races to so much lower an average than that of more civilised peoples. It then occurred to me that these causes, or their equivalents, are continually acting in the case of animals also; and as animals usually breed much more rapidly than does mankind, the destruction every year from these causes must be enormous in order to keep down the numbers of each species, since they evidently do not increase regularly from year to year, as otherwise the world would long ago have been densely crowded with those that breed most quickly.