A recent writer says of Professor Charles Eliot Norton that he was "not of a rugged constitution, yet he did an enormous amount of work and lived to a beautiful old age." This is attributed to the fact that he was never "blue." The cheerful kindliness of his face, his genial smile and kind words were sources of great inspiration to me when a teacher at Harvard, and to all who met him. The more we investigate the theories of long life the more do we become impressed with a universal longing for a length of days. We find a deep, underlying instinct "that men do not live out half their days." Everywhere, too, we find a certain expectation of "finding the fountain of youth," a hope in some way to conquer sickness and death. This desire is normal and natural. It may, sometime in future history, be realized. As we examine these theories we find, however wild they may seem at first, certain common sense views at the heart of all of them. No one need make a hobby of any one of them. Temperance, regularity, repose, patience, and above all, cheerfulness, do not exclude each other, they rather imply one another. In many instances one can hardly be practiced without some of the others. The practice of one would unconsciously bring up the others. If we study carefully these theories, and especially if we study the lives of those who have not only professed theories but have faithfully practiced their principles and attained great health and age, we always find a combination of various methods. There is no doubt, for example, that Cornaro completely reformed his life. The character of Socrates was the secret of his good health. Temperance to the Greek did not mean total abstinence. It meant lack of extravagance; it meant what we mean by patience, by an unruffled temper,--it meant the right use of all the faculties and powers. What new hobby, you may ask, is the theme of this book? Nothing that will interfere with the fundamental elements of the best ideas of all ages. First of all it is advocated that we go down deeper into all theories. Temperance should not be applied merely to food and drink but must cover self-control, repose of life, purity and depth of thought, and a harmonious development of human nature. The book tries to draw attention to many important things which are usually overlooked or not considered necessary to health and life. The study of expression, to choose only one example, reveals to us, the necessity of a right poise of the body. One of the leading teachers of science in this country, after fighting tuberculosis for three years, changing climates and using all the help that science has provided, determined at last to go back to his work and to do his best even though he lost his life.