1887.] NEW YORK ACADEMY OF SCIENCES. 99 



turned his attention to producing glass discs of the requisite 

 purity for making hirge telescopes, "He obtained some flint 

 glass from England, but this Avas not always perfectly pure. 

 He melted it anew, but did not obtain satisfactory glass." He 

 then erected an establishment in which he constructed Avith his 

 own hands a very large furnace, and commenced the manufac- 

 ture of glass; and finally succeeded in obtaining pieces large 

 enough for telescopes. He afterwards discovered a method of 

 softening pieces of perfectly pure glass for the purpose of giving 

 them the form of a disc. In 1805 he was employed by Utz- 

 schneider to assist in making object-glasses at the celebrated 

 optical estabishment near Munich, Here he worked with Fraun- 

 hofer, but in a subordinate capacity. He had sold his secret 

 with his service. After remaining here some nine years he re- 

 turned home, drawing a pension from the Munich establishment 

 so long as he did not reveal the secret or himself make object- 

 glasses. 



He could not long resist the temptation, and soon gave up 

 the pension to undertake the manufacture of larger discs than 

 any he had previously made. In 1823 he produced a disc 18 

 inches in diameter. In 1824 he exhibited at the exposition in Paris 

 a grand achromatic object-glass which excited the admiration of 

 the king, and Guinand was invited to come to Paris to live. He, 

 however, was in feeble health and old. He died in 1825 at the 

 advanced age of nearly 80 years. Many think that Fraunhofer 

 owed to Guinand much of his fame gained in making large 

 object-glasses. 



After the death of Guinand, his widow and one of his sons set 

 up works in Switzerland. The other son was introduced to Bon- 

 temps of Paris. They succeeded in producing good flint glass in 

 discs of from 12 to 14 inches in diameter. In 1848 Bontemps 

 accepted an invitation to unite with Messrs. Chance Bros. & Co., 

 of Birmingham, England, in their efforts to improve the quality 

 of glass. 



They have succeeded in producing some very large discs, 

 notably the ones for the Newall telescope of 25 inches, and also 

 the discs for the great Washington telescope of 26 inches diam- 

 eter, Tiie establishment of Guinand at Paris is now conducted 



