Faraday acknowledged that he was often compelled to give up his preconceived notions, and in some cases his failures are almost as instructive as his discoveries. It was characteristic of him to hold to his theories until he proved them either true or false, and he was ever ready to reject any hypothesis as soon as he found it inconsistent with the laws of nature. Newton was willing to suspend judgment for years upon his theory of gravitation, until more accurate measurements of the earth’s size and the moon’s distance showed his theory and calculations to be right. Socrates advised his followers to quit the study of astronomy, probably because he felt that in his time the data were not sufficient to warrant definite conclusions. Hosts of instances can be cited showing that the thinking of the strongest intellects does not issue in knowing when it is based upon or biassed by a wrong working hypothesis. And yet it must be confessed that wrong hypotheses may lead to valuable negative results, as in the case of Kepler’s investigations, each exploded theory making room for the construction of a theory more in accordance with the facts. The superiority of men of genius lies in their love of truth and fidelity to fact; in the facility with which they construct theories to account for observed phenomena; in the patience with which they test theory by fact, and in the readiness with which they reject every hypothesis as soon as it is found to be in irreconcilable conflict with well-established facts. The average life of a theory in science is said to be only ten years. The average would be lower still if all rejected theories had been put into books. The men possessed of a truly scientific spirit differ from ordinary men not only in the painstaking accuracy of their observations and in the surprising fertility with which they frame theories, but also in the habit of verifying every hypothesis until there is sufficient ground to establish its truth and to receive it as an addition to the sum total of human knowledge.
The common people are quite as ready to frame theories as the scientists and philosophers. It would be well if they were equally patient in testing their theories and in verifying their suppositions. The human mind cannot help generalizing. The moment a child uses a common noun it begins to classify. Its tendency to pull things to pieces and to put them together again are exhibitions of the mind’s tendency to treat everything by analysis and synthesis. Purpose and design, cause and effect early show themselves in the thinking of children. The teacher need but guide these activities and give the mind the proper material to work upon; the result cannot be doubtful if the mind which plays upon the learner’s mind has been trained to operate according to the laws of thought and the principles which must guide in the discovery of the truth.