It is important to recognize that there is nothing mysterious in the method of science, or apart from the ordinary routine of life. Science has been defined as the habit or faculty of observation. By such the child grows in knowledge, and in its daily exercise an adult lives and moves. Only a quantitative difference makes observation scientific--accuracy; in that way alone do we discover things as they really are. This is the essence of Plato's definition of science as "the discovery of things as they really are," whether in the heavens above, in the earth beneath, or in the observer himself. As a mental operation, the scientific method is equally applicable to deciphering a bit of Beneventan script, to the analysis of the evidence of the Commission on Coal-Mines, a study of the mechanism of the nose-dive, or of the colour-scheme in tiger-beetles. To observation and reasoned thought, the Greek added experiment, but never fully used it in biology, an instrument which has made science productive, and to which the modern world owes its civilization. Our every-day existence depends on the practical application of discoveries in pure science by men who had no other motives than a search for knowledge of Nature's laws, a disinterestedness which Burnet claims to be the distinctive gift of Hellas to humanity. With the discovery of induced currents Faraday had no thought of the dynamo. Crookes's tubes were a plaything until Roentgen turned them into practical use with the X-rays. Perkin had no thought of transforming chemical industry when he discovered aniline dyes. Priestley would have cursed the observation that an electrical charge produced nitrous acid had he foreseen that it would enable Germany to prolong the war, but he would have blessed the thought that it may make us independent of all outside sources for fertilizers.