"[I]t is one of the mistakes of scholars to believe that they are the sole transmitters of knowledge. ...[T]he characters, the methods of calculating, the improvements that took place from time to time, the zero when it appeared, and the customs as to solving business problems, would all have been made known from generation to generation along... trade routes from the Orient to the Occident. [I]t was to the tradesman and the wandering scholar that the spread of such learning was due, rather than to the school man."