It is a commonplace of the lecturer on popular science at the present day, that the impulse to the development of our modern scientific discoveries which became so marked toward the end of the eighteenth century, was due in a noteworthy degree to the work of the French Encyclopedists. Their bringing together of all the details of knowledge in a form in which it could be readily consulted, and in which previous progress and the special lines of advance could be realized, might be expected to prove a fruitful source of suggestive investigation. As a matter of fact, however, a detailed knowledge of the past in science often seems to be rather a hindrance than a help to original genius, always prone to take its own way if not too much disturbed by the conventional knowledge already gained. Most of the great discoverers in science were comparatively young men when they began their careers as original investigators; and it was apparently their freedom from the incubus of too copious information that left their minds untrammelled to follow their own bent in seeking for causes where others had failed to find any hints of possible developments. This was certainly the case with regard to many of those distinguished founders who lived in centuries prior to the nineteenth. Most of {173} them were men under thirty years of age, and not one of them had been noted, before he began his own researches, for the extent of his knowledge in the particular department of science in which his work was to prove so fruitful. Their lives illustrate the essential difference there is between theory and observation in science. The theorizer reaches conclusions that are popular as a rule in his own generation, and receives the honor due to a progressive scientist; the observer usually has his announcements of what he has actually seen scouted by those who are engaged in the same studies, and it is only succeeding generations who appreciate how much he really accomplished. This was especially exemplified in the case of the Abbé Haüy, whose work in crystallography was to mean so much. What he learned was not from books, but from contact with the actual objects of his department of science; and it is because the example of a life like this can scarcely fail to serve a good purpose for the twentieth-century student, in impressing the lesson of the value of observation as opposed to theory, that its details are retold. Réné Just Haüy was born 28 February, 1743, in the little village of Saint-Just, in the Department of Oise, somewhat north of the center of France. Like many another great genius, he was the son of very poor parents. His father was a struggling linen-weaver, who was able to support himself only with difficulty. At first {174} there seemed to be no other prospect for his eldest son than to succeed to his father's business. Certainly there seemed to be no possibility that he should be able to gain his livelihood by any other means than by the work of his hands.