Some Account of the late M. Gui7iand. 247 



the small number of works he was able to procure, which treated 

 on subjects connected with optics. 



Meanwhile the ingenious and important discovery of achromatic 

 glasses was beginning to spread ; and having reached that 

 country, it could not fail to be very interesting to M. Guinand, 

 who listened with avidity to all that he heard on this subject. 

 M. Jacquet Droz, having procured one of these new glasses, per- 

 mitted M. Guinand, as in the iastance of the reflecting telescope, 

 to take it to pieces, and to separate the lenses. It will readily be 

 conceived that the purpose of the latter was to attempt the con- 

 struction of a similar instrument, but in this he was impeded, by 

 the difficulty of procuring glasses of different refractive power. 

 It was not until some years afterwards that an acquaintance of 

 his, M. Recordon, having proceeded to England, where he obtained 

 a patent for his invention of self-winding watches, which were 

 then in great request, brought him from that country some 

 flint-glass ; and though the specimen was much striated, he found 

 means to manufacture from it some tolerably good achromatic 

 glasses. Having obtained supplies of this material on various 

 occasions, and having seen other glasses besides those of M. Ja- 

 quet Droz, he easily ascertained that flint-glass, which is not ex- 

 tremely defective, is rarely to be met with. Thus convinced of 

 the impossibility of procuring it of that quality which he ardently 

 wished to obtain for the construction of his telescopes, and having 

 by his various labours become sufficiently skilled in the art of 

 fusion, he melted in his blast furnace the fragments of this flint- 

 glass ; no satisfactory result was obtained, but he discovered 

 from some particles of lead, which re-appeared during the pro- 

 cess, that this metal was a constitutent in the composition of flint- 

 glass. At the time of this first experiment he had attained his 

 thirty-fifth or thirty-sixtli year. The ardent desire to obtain 

 some of this glass then induced him to collect from the different 

 works he was able to procure, such notions of chemistry as might 

 be useful to him in his attempts at vitrification; and during six 

 or seven years (from 1 7S4 to 1 790) he employed a part of his 

 evenings in different experiments, melting at each time in bis 



