The huge advances in human knowledge and technical achievement of recent years have ushered in an age of specialisation. Each branch of industry embraces such a variety of facts of its own that a full knowledge of the whole field of endeavour is beyond the reach of any one man. That fact becomes every day more patent as intensive study in special fields extends the scope of every industry to which it is applied. Every newspaper contains advertisements setting forth the value of various highly technical courses for people in almost every walk of life.

All this indicates the growing value of brains and the product of brains. The mind is an instrument for the doing of its own kind of work. Like other instruments it gives the best return when trained and finely adjusted for carrying out its functions. Just as, on the physiological side, certain results are obtained by special attention to certain functions, e.g. improved health from physical training, and athletic prowess from intensive training, so, in the sphere of psychology, that is, the sphere of the mind and the will, the best results are to be obtained only after the mental powers have been trained and the powers of the will have been brought under control.