The Abbé's recreation consisted in botanizing expeditions; and Haüy, who had chosen the kindly old priest as his spiritual director, was his most frequent companion. Occasionally, when M. Lhomond was ailing, and unable to take his usual walks, Haüy spent the time with him. He rather regretted the fact that he did not know enough about botany to be able to make collections of certain plants to bring to the professor at such times, in order that the latter might not entirely miss his favorite recreation. Accordingly, one summer when he was on his vacation at his country home, he asked one of the Premonstratensian monks, who was very much interested in botany, to teach him the principles of the science, so as to enable him to recognize various plants. Of course his request was granted. He expected to have a pleasant surprise for Abbé Lhomond on his return, and to draw even closer in his friendly relations with him, because of their mutual interest in what the old Abbé called his scientia amabilis (lovely science). His little plan worked to perfection, and there was won for the study of physical science a new recruit, who was to do as much as probably any one of his generation to extend scientific knowledge in one department, though that department was rather distant from botany.
Haüy's interest in botany, however, was to [{177}] prove only temporary. It brought him in contact with other departments of natural history, and it was not long before he found that his favorite study was that of minerals, and especially of the various forms of crystals. So absorbed did he become in this subject that nothing pleased him better than the opportunity to spend long days in the investigation of the comparative size and shape of the crystals in the museum at Paris. A friend has said of him that, whether they were the most precious stones and gems or the most worthless specimens of ordinary minerals, it was always only their crystalline shape that interested Haüy. Diamonds he studied, but only in order to determine their angles; and apparently they had no more attraction for him than any other well-defined crystal--much less, indeed, than some of the more complex crystalline varieties, which attracted his interest because of the difficulty of the problems they presented.
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.
By his studies, however, Haüy was able to determine that whenever substances of the same composition crystallized, even though the external form of the crystals seemed to be different, all of them were found to have the same internal nucleus. Whenever the mineral under observation was chemically different from another, then the nucleus also had a distinctive character; and so there came the law that all substances of the same kind crystallized in the same way, notwithstanding apparent differences. Indeed, one of the first results of this law was the recognition of the fact that when the crystalline forms of two minerals were essentially different, then, no matter how similar they might be, there was sure to be some chemical difference. This enabled Haüy to make certain prophecies with regard to the composition of minerals.
A number of different kinds of crystals had been classed together under the name of [{180}] heavyspar. Some of these could not, by the splitting process, be made to produce nuclei of similar forms, and the angles of the crystals were quite different. Haüy insisted that, in spite of close resemblances, there was an essential distinction in the chemical composition of these two different crystalline formations; and before long careful investigation showed that, while many of the specimens called heavyspar contain barium, some of them contain a new substance--strontium--which had been very little studied heretofore. This principle did not prove to be absolute in its application; but the amount of truth in it attracted attention to the subject of crystallography because of the help which that science would afford in the easy recognition of the general chemical composition of mineral substances. The most important part of Haüy's work was the annunciation of the law of symmetry. He emphasized the fact that the forms of crystals are not irregular or capricious, but are very constant and definite, and founded on absolutely fixed and ascertainable laws. He even showed that, while from certain crystalline nuclei sundry secondary forms may be derived, there are other forms that cannot by any possibility occur. Any change of crystalline form noticed in his experiments led to a corresponding change along all similar parts of the crystal. The angles, the edges, the faces, were modified in the same way, at the same time. All these elements of mensuration within the crystal Haüy thought could be indicated by rational coefficients.
Crystallography, however, did not absorb all Haüy's attention. He further demonstrated his intellectual power by following out other important lines of investigation that had been suggested by his study of crystals. It is to him more than to any other, for instance, that is due the first steps in our knowledge of pyro-(or thermo-) electricity. Mr. George Chrystal, professor of mathematics at the University of St. Andrews, in the article on electricity written for the ninth edition of the Encyclopedia, says it was reserved for the Abbé Haüy in his Treatise on Mineralogy to throw a clear light on this curious branch of the science of electricity.
To those who are familiar with the history of the development of this science it will be no surprise to find a clergyman playing a prominent role in its development. During the days of the beginning of electricity many ecclesiastics seem to have been particularly interested in the curious ways of electrical phenomena, and as a consequence they are the original discoverers of some of the most important early advances. Not long before this, Professor Gordon, a Scotch Benedictine monk who was teaching at the University of Erfurt, constructed the first practical electrical machine. Kleist, who is one of the three men to whom is attributed the discovery of the principle of storing and concentrating electricity, and who invented the Leyden Jar, which was named after the town where it was first manufactured, was also a member of a Religious Order. As [{182}] we have already stated, Dirwisch, the Premonstratensian monk, set up a lightning-conductor by which he obtained sparks from the clouds even before our own Franklin.