construction of perfect optical instruments. With this result, satisfactory as it would have been to most men, Guinand expressed himself by no means contented, and continued his researches, without, however, ever arriving much nearer to perfection in the art. He was now enabled to make use of, for discs, glass perfectly homogeneous, with a diameter of twelve inches: a great achieve. ment, when compared with what had been at any time accomplished by others.

A year or two before his death, he tried an experiment on a larger scale than any he had previously attempted. After much trouble and exertion, he succeeded in obtaining a disc of eighteen inches in diameter, of perfectly homogeneous glass. The disc had been put into the oven for the last time, to be gradually cooled: and the operation being now considered as completed, his friends and neighbors were admitted, and partook of some refreshment ; while offering their congratulations on his unprecedented success after so long a seclusion, the fire by some accident or neglect caught the roof of the building. On this alarming occasion all present exerted themselves, and after some trouble the flames were extinguished; but not before some water had found its way into the oven and destroyed its precious contents. The discouragement caused by this misfortune, and some other circumstances, ever after prevented him from any experiment on a similar scale.

For some time after he had thus far succeeded in his object, he was accustomed to divide his blocks of glass by that which appeared to be the only fitting method, sawing them into sections perpendicular to their axis, polishing their sections, and then selecting such parts as were adapted to his purpose, returning the remaining portion to the crucible for farther operations. By this means he had frequently the mortification of perceiving, that the glass was divided so as to present a less extended surface of the perfect material, than the state of the block would, if previously known, have rendered possible; and he was frequently able to procure discs of only small diameter, when, could he have been fully aware of the particular circumstances of the glass throughout its substance, he might, by cutting in another direction, have obtained a more satis. factory result.

This disadvantage was remedied in a way apparently as untoward as it was singular and unexpected. While his men were carrying one day a block of glass on a handbarrow to a water saw. mill, which he had constructed at the fall of the river Doubs, a short distance from his dwelling, the mass accidentally slipped, and rolling to the bottom of a rocky declivity, was broken into several pieces. Endeavoring to make the best of this seeming misfortune,

such fragments of glass were selected for operation as appeared to be fitted by their homogeniety for the purpose; and these were softened in circular moulds, in such a manner that they furnished discs of a very satisfactory quality. Further examination enabled him to perceive that the fracture had in a great measure followed the variations of density in the glass; and, pursuing the idea thus obtained, the artist thenceforth adhered to a method so singularly in the first instance forced upon him.

After this, he contrived a mode of cleaving the glass while cool. ing, so that the fracture accompanied the direction of the more faulty parts; by which course he frequently obtained masses of glass which were absolutely homogeneous, weighing from forty to fifty pounds. These masses, cleft again by means of wedges into pieces of convenient shape, were remelted into moulds which gave them the form of discs; an operation which differs essentially from that used by other glass makers.

Several years of his life were thus employed in making bells for repeating watches and constructing achromatic telescopes with glass of his own preparing. The retired spot wherein he resided, offered only very limited opportunities for acquiring a reputation in the world; yet, by degrees, the superior value of his labors became appreciated, and he was visited by such men of science as travelled in the neighborhood of his dwelling. By one of these a knowledge of his merits was conveyed to M. Frauenhofer, the chief of a celebrated manufactory for optical instruments, estab. lished at Benedictbeurn, in Bavaria. This gentleman having, in consequence, obtained some discs of glass made by Guinand, found their quality so satisfactory, that he repaired in person to Brenets, where Guinand resided, and engaged him to settle in Bavaria. This was in 1805, when Guinand was upwards of sixty years of age. He continued at this place during nine years, occupied solely in the manufacture of glass, to the great increase of his employer's reputation.

Being desirous, at the end of this time, to return to his native land, a pension was granted to him by the establishment, on condition that he should no longer employ himself in making glass, nor disclose his process to any person whatever; a condition which did not long agree with the still active energies of his mind. Believing, by new experiments, he could raise his discovery to a yet higher degree of improvement, he obtained the consent of Frauenhofer, to cancel their subsisting agreement; and, relinquishing his pension, once again devoted himself with ardor to his favorite pursuit.

He lived seven years after this time, and produced several

telescopes of great magnitude, and remarkable for their excellence; it being perhaps not the least extraordinary among the circumstances attending them, that, to use the words of the memoir from whence the foregoing account is drawn, "they have been constructed by an old man upwards of seventy, who himself manufactures the flint and crown glass which he uses in their construction, after having made, with his own hands, the vitrifying furnace and his crucibles; who, without any mathematical knowledge, devises a graphic method of ascertaining the proportions of the curves that must be given to the lenses, afterwards works and polishes them by means peculiar himself, and lastly, constructs all the parts of the different mountings either with joints or with stands, melts and turns the plates, solders the tube, prepares the wood, and compounds the varnish.”

M. Guinand died in 1823, in his eightieth year. The preceding pages show how greatly his loss is to be deplored. After half a century of research, he was the only man in Europe who had succeeded in obtaining large specimens of that flint glass which is so indispensable for the construction of achromatic lenses, and at the same time so difficult to obtain free from striæ in any considerable magnitude. Arrangements had been made by the French government for purchasing his secret at the time of his death. In the latter part of his life he was assailed by infirmities incident to his multifarious labors and advanced age. It is to be lamented, that after sacrificing so much to his art, so much more than could have been expected from a man in his circumstances, he should derive from them so little advantage; and lastly, it is painful to think that this man, in attaching so little importance to the honor of his discovery, should not have made it more extensively known, and connected it more closely with his name; since it is a discovery which, by the perfection it imparts to telescopes, opens the way to very important acquisitions in the vast field which the heavens still offer to optical instruments in a state of perfection. The secret, however, did not die with him, but is possessed by his son, who continues to labor in the employment so singularly commenced, and so energetically and successfully followed by the father.