This acute analysis, sufficiently surprising in a young man of twenty years, suggests in an admirable manner the conditions necessary to the highest manifestations of the intellect. It carries a lesson which, if it were sufficiently understood, would facilitate the way of all contemplative spirits capable of opening new paths for humanity. The unity of thought toward which Pierre Curie strove was troubled not only by professional and social obligations but also by his tastes, which urged him towards a broad literary and artistic culture. Like his father, he loved reading, and did not fear to undertake arduous literary tasks. To some criticism made in this connection, he responded readily: "I do not dislike tedious books." This meant that he was fascinated by the search after truth which is sometimes associated with writing devoid of charm. He also loved painting and music, and went gladly to look at pictures or to attend a concert. A few fragments of poetry in his handwriting were left among his papers. But all these preoccupations were subordinated in his mind to what he considered his true task, and when his scientific imagination was not in full activity, he felt himself, in a sense, an incomplete being. He expressed this inquietude with an emotion born of his suffering during momentary periods of depression. "What shall I become?" he wrote. "Very rarely have I command of all myself; ordinarily a part of me sleeps. My poor spirit, are you then so weak that you cannot control my body? Oh, my thoughts, you count indeed for very little! I should have the greatest confidence in the power of my imagination to pull me out of the rut, but I greatly fear that my imagination is dead." But despite hesitations, doubts, and lost moments, the young man was little by little striking out his path and strengthening his will. He was resolutely carrying on fruitful investigations at an age when many men who were to become savants were as yet only pupils. His first work, done in collaboration with Desains, concerned the determination of the lengths of heat waves with the aid of a thermoelectric element and a metallic wire grating, a process, then entirely new, which has since often been employed in the study of this question.