It has been frequently said that many of the world’s greatest inventions were due to accident. In a sense this is true. But the accident was prepared for by previous hard thinking. It would never have occurred had not this thinking taken place. It is said that the idea of gravitation came to Newton because an apple fell on his head. Perhaps. But apples had been falling ever since there were apple trees, and had probably been falling on men’s heads ever since men had acquired the habit of getting their heads in the way. The idea of the steam engine is supposed to have come to Watt while observing a tea kettle. But how many thousands before him had not seen steam coming out of kettles? The idea of the pendulum for regulating time occurred to Galileo from observing a swinging lantern in a cathedral. Think how many others must have seen that lantern swinging! It is probable that in all these cases the invention or idea had been prepared for, had been all but formed, by downright hard thinking in previous periods of concentration. All that was needed was the slightest unusual occurrence to make the idea complete and conscious. The unusual occurrence, the accident, which has so often received the credit for the invention or the idea, merely made it come sooner, for with the thinking these men did, it was bound to come eventually. . . . Of course I really do not seriously expect anybody to concentrate at every opportunity. I don’t myself. I merely wanted to establish the fact that it’s the best thing. But every man, even the tired business variety, should set aside at least half an hour a day, or three and a half hours a week. I realize what a great hardship it is for some people to devote one-forty-eighth of their time to such a useless pastime as thinking. But if they will make the sacrifice for seven consecutive days they will find themselves bearing up nobly at the end. There is even a possibility that they may be encouraged to extend the time. V PREJUDICE AND UNCERTAINTY