Like many another advance in science, Haüy's first great original step in crystallography was the result of what would be called a lucky accident. These accidents, however, be it noted, happen only to geniuses who are capable of taking advantage of them. How many a man had seen an apple fall from a tree before this little circumstance gave Newton the hint from which grew, eventually, the laws of gravity! Many a man, doubtless, had seen little boys tapping on logs of wood, to hear how well sound was {178} carried through a solid body, without getting from this any hint, such as Laennec derived from it, for the invention of the stethoscope. So, too, many a person before Haüy's time had seen a crystal fall and break, leaving a smooth surface, without deriving any hint for the explanation of the origin of crystals. According to the familiar story, Haüy was one day looking over a collection of very fine crystals in the house of Citizen Du Croisset, Treasurer of France. He was examining an especially fine specimen of calcspar, when it fell from his hands and was broken. Of course the visitor was much disturbed by this accident. His friend, however, in order to show him that he was not at all put out at the breaking of the crystal, insisted on Haüy's taking it with him for purposes of study, as they had both been very much interested in the perfectly smooth plane of the fracture. As Haüy himself says, this broken portion had a peculiarly brilliant lustre, "polished, as it were by nature," as beautifully as the outer portions of the crystal; thus demonstrating that in building up of so large a crystal there must have been certain steps of progress, at any of which, were the formation arrested, smooth surfaces would be found. On taking the crystal home, Haüy proceeded further to break up the smaller fragment; and he soon found that he could remove slice after slice of it, until there was no trace of the original prism, but in place of it a rhomboid, {179} perfectly similar to Iceland spar, and lying in the middle of what was the original prism. This fact seemed to him very important. From it he began the development of a theory of crystallization, using this observation as the key. Before this time it had been hard for students of mineralogy to understand how it was that substances of the same composition might yet have what seemed to be different crystalline forms. Calcspar, for instance, might be found crystallized in forms, apparently, quite at variance with one another.