time a very fine reflecting telescope which had been made in England, and which at once appeared to him so curious and interesting an object, that he petitioned for and obtained leave to take it in pieces, the more minutely to examine its construction. The use made

of this permission was soon rendered apparent by the production of a similar telescope; and this, which he had constructed with his own hands, on being examined by many competent persons, was pronounced by them to be equal in excellence to that which had served him as a pattern.

Surprised at this success, the gentleman to whose kindness he owed this opportunity questioned the artist as to his acquaintance with the science of optics, and in particular to what treatise he was indebted for his proficiency. The surprise of M. Droz was naturally increased on learning that the instrument had been produced without any knowledge whatever of the theory of optics, and with no more acquaintance with the practice of the art than had been acquired through the examination of the English instrument. M. Droz immediately placed a treatise on the subject in the hands of the young man, which he rather deciphered than ́read; but the substance of which was imbibed by him so completely, that he was enabled, after witnessing the making of one pair of spectacles, to form and polish lenses, and to make spectacles for himself and others, which were pronounced to be excellent. His principal amusement at this time was found in manufacturing telescopes, which he got up at a cheap rate, forming the tubes of pasteboard.

When the important discovery of achromatic glasses reached Switzerland, Guinand's mind was very strongly excited by it; and M. Droz having obtained a telescope of the new construction, again permitted the young man to examine its various parts and structure. The very imperfect state of the arts at that time in Switzerland, and the deficient means of Guinand, prevented his achieving the construction of a similar instrument. He was unable to produce glasses of different refractive

power; and it was not until several years afterwards that an acquaintance, making a visit to England, conveyed to him a piece of flint glass, with which, although it was by no means void of imperfections, being considerably striated, he succeeded in making some tolerably good achromatic glasses. Finding that not only the glass which he had himself worked, but that every other specimen which he examined was thus imperfect, he was incited to a more particular scrutiny into the subject, and bringing into action all the knowledge he had acquired in the art of fusion, he melted in his furnace the fragments of his flint glass. All the satisfaction derived from this experiment was the acquirement of some degree of knowledge as to the composition of flint glass, some particles of lead being revived in the metallic state during the process. Guinand was thirty-five years old at the time when this fresh incitement led to his seeking after such chemical knowledge as might assist him in experiments on vitrification, and his evenings' employment during six or seven years was to melt in his blast furnace a few pounds' weight of glass, carefully noting down every circumstance attending each experiment, that he might be enabled to continue such as afforded any prospect of advantage, and to avoid others which had a contrary tendency.

These small experiments led to no decisive results; and he was upwards of forty years old when, having undertaken a new and more profitable trade, that of making bells for repeating watches, he was enabled to devote more of his earnings to the prosecution of experiments, which he thenceforth undertook upon a scale more likely by their results to reward his perseverance.

In this pursuit he was still exposed to numerous accidents and difficulties, which would have deterred most persons from continuing the research. His furnace, which he had constructed with his own hands, out of such materials as he could procure, and which was capable of melting at once 200 lbs. weight of glass, proved defective. He was then obliged to procure materials for

the purpose from abroad; and having once more completed its erection, and consumed much fuel in heating it, had the mortification to find that it still required alteration. Then his crucibles, which he was equally obliged to form with materials ill-qualified for the object, cracked during the process, and the vitreous matter was lost among the ashes of his furnace. Although during all this time his family arrangements were formed upon a plan of the most rigid economy, he was compelled to employ an interval between each one of his experiments in earning at his regular employment sufficient means for subsistence, and for providing the apparatus, materials, and fuel needful for renewing them.

All this time the pursuit had laid hold so completely of his mind, that he was deprived of his natural rest while considering upon the causes of his various failures, and endeavouring to reason out the means for their prevention.

Having at length succeeded in obtaining a block of glass weighing about 200 pounds, and having sawn it into two vertical sections, he polished one of the faces, in order, as far as possible, to examine the circumstances produced by the fusion.

To account for the numerous and various defects exhibited by this specimen, M. Guinand formed a theory which he made the groundwork of his future operations. A more intimate knowledge of those defects, and a conviction thus attained of the great difficulties opposed to their removal, instead of damping his ardour in the pursuit, served to infuse new energy into his mind. Nor was he mistaken in his estimate of the obstacles to be surmounted; so that," as he himself declared, "the sacrifices and exertions which he had previously made were trifling when compared with those which he afterwards underwent for the purpose of removing these various defects, and of rendering his glass homogeneous."

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The steps through which he pursued this arduous undertaking, and the methods by which its success was accomplished, it is not possible to detail. All that is

publicly known upon the subject is, that he succeeded in discovering a mode of proceeding which gave the almost certainty of producing in the fusion of a pot containing from 200 to 400 pounds of glass, one half at least of its substance entirely homogeneous, and therefore fitted for the 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 for use discs of glass perfectly homogeneous, with a diameter of twelve inches; a great achievement, when compared with what had been at any time accomplished by others.

On one occasion the artist had succeeded, through much carefulness and exertion, in obtaining a disc eighteen inches in diameter, and of a quality perfectly satisfactory. This was already finished and placed in the annealing oven to cool gradually, when, through some unaccountable accident the fire caught the roof of his humble dwelling. With some trouble the flames were extinguished; but the water used for this purpose had found its way into the oven, and the precious deposit was destroyed. It is said that the discouragement caused by this accident prevented M. Guinand from afterwards attempting any similarly extensive experiment. He entertained no doubt, however, that, with means for operating on a larger scale than he could accomplish, lenses of double or even triple the diameter here mentioned might be produced.

For some time after he had thus far succeeded in his object, M. Guinand was accustomed to divide his blocks of glass by that which appeared the only fitting method, sawing them into sections perpendicular to their axis, polishing the sections, and then selecting such parts as were adapted to his purpose, returning the remaining portions to the crucible for future operations. By this means he had frequently the mortification of perceiving that the glass was divided, so as to present a less ex

tended surface of 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 satisfactory result.

This disadvantage was remedied in a way apparently as untoward as it was singular and unexpected. While his men were one day carrying a block of glass on a hand-barrow to a water sawmill, which he had constructed at the fall of the river Doubs, a short distance from his dwelling, the mass accidently slipped, and, rolling to the bottom of a rocky declivity, was broken into several pieces. Endeavouring to make the best of this seeming misfortune, such fragments of glass were selected for operation as appeared to be fitted by their homogeneity 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 Guinand 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, M. Guinand contrived a mode of cleaving the glass while cooling, 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 in 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 by this extraordinary man 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