914 Impurity of Puherized Emetid of Tartar, 



in so active a medicine is of the utmost importance, 1 would ear- 

 nestly recommend my brethren of the profession to purchase this 

 article always in crystals. By the insertion of these observations 

 you will much oblige, 



Sir, your obedient servant, 



An Old Practitioner. 



Art. XI. — Some Account of the late M. Guinand, Optician 

 of Brenets, in the Canton of Neufchatel, in Switzerland, 

 read at the Society of Physics and Natural History of 

 Geneva, on the I9th of February, 1823 *. 



The Society of Physics and Natural History of Geneva, and the 

 Class of Industry in the Society of Arts of that city, having testi- 

 fied in the most flattering manner their approbation of the speci- 

 mens oifiint glass ^ made by M. Guinand, and submitted to their 

 inspection by M. Houriet ; and having expressed a desire to pos- 

 sess some details on the origin of his establishment, they are given 

 with much pleasure in the following notice, which is with greater 

 confidence presented, as M. Guinand himself communicated the 

 principal part of the facts which it contains. 



* When the present memoir was addressed to the Society, the interesting 

 artist to whom it relates, was still living, but the intelligence of his decease 

 (at the close of 1828,) was communicated at the same time with the history of 

 liis labouTs. The following pages will show how greatly sucli a loss is to be 

 deplored. After half a century of research, M. Guinand was the only man in 

 Europe who had succeeded in producing large specimens of that Jlint glass 

 which is so indispensable for the construction of achromatic lenses, and at the 

 same time so difficult to obtain, free from strise, in pieces of any considerable 

 magnitude. Arrangements had been made by the French government for 

 purchasing his secret, when the artist, verging on his eightieth year,, died after 

 a short illness. His son remains in possession of his process, and it is said 

 that he will continue to supply opticians with flint-glass necessary for object- 

 lenses of large apertures, the only ones which collect sufficient light, and 

 which produce a sufficiently exact convergence of the rays to allow 'he appli- 

 cation of eye-pieces of a very short focus, or, in other words, to give them a 

 considerable degree of amplifying power. 



