The want of energy is one of the main reasons why so few persons continue to improve in later years. They have not the will, and do not know the way. They 'never try an experiment,' or look up a point of interest for themselves; they make no sacrifices for the sake of knowledge; their minds, like their bodies, at a certain age become fixed. Genius has been defined as 'the power of taking pains'; but hardly any one keeps up his interest in knowledge throughout a whole life. The troubles of a family, the business of making money, the demands of a profession destroy the elasticity of the mind. The waxen tablet of the memory which was once capable of receiving 'true thoughts and clear impressions' becomes hard and crowded; there is not room for the accumulations of a long life (Theaet. 194 ff.). The student, as years advance, rather makes an exchange of knowledge than adds to his stores. There is no pressing necessity to learn; the stock of Classics or History or Natural Science which was enough for a man at twenty-five is enough for him at fifty. Neither is it easy to give a definite answer to any one who asks how he is to improve. For self-education consists in a {ccxi} thousand things, commonplace in themselves,--in adding to what we are by nature something of what we are not; in learning to see ourselves as others see us; in judging, not by opinion, but by the evidence of facts; in seeking out the society of superior minds; in a study of lives and writings of great men; in observation of the world and character; in receiving kindly the natural influence of different times of life; in any act or thought which is raised above the practice or opinions of mankind; in the pursuit of some new or original enquiry; in any effort of mind which calls forth some latent power.