As in all my other books I have used plain, honest English. Not any plainer than necessary, but plain enough to avoid obscurity and misconception. Science and art are both necessary to human happiness. This is not the place to discuss the rela tive importance of the two. And, while I have no patience with art-for-art's-sake, I recognize that the scientist can not be put into a narrow channel and ordered to go into a certain definite direction. Seien tific investigations which seemed aimless and useless have sometimes led to highly important results, and I would not disparage science for its own sake. It has its uses. Nevertheless I personally have no use for it. To me everything must have a direct human purpose, a definite human application. When the cup of human life is so overﬂowing with woe and pain and misery, it seems to me a narrow dilettante ism or downright charlatanism to devote one's self to petty or bizarre problems which can have no rela tion to human happiness, and to prate of self-satis faction and self-expression. One can have all the self-expression one wants while doing useful work.