The extensive development undergone by the most exact of all the sciences during the past century, and particularly during the last quarter of a century, has found expression not only in a wealth of new knowledge but also, and equally, in a transformation of its working methods. It may be this transfiguration that holds particular attractions for the observer interested more in the picture as a whole than in the individual details. It is, indeed, sometimes possible to gain deeper insights into a science through a glance at its methods than through a summary of its material results, for such insights reveal the evolution of the very mechanisms of human thought.