384 



HISTORY OF ASTKONOMY. 



8 inches diameter, 19 15s. 



9 " " 22 10 



9 " 25 10 



10 " " 28 10 

 10i " " 31 10 



11 " 35 00 

 H " " 39 10 



12 inches diameter, 44 OOs. 

 12$ " " t 50 00 



13 " " 57 15 

 13$ " " 65 00 



14 " " 75 00 

 14$ " " 85 00 



15 " " 100 00 



M. Maes, of Clichy, near Paris, exhibited at the Lon- 

 don, and also at the New York Expositions, specimens 

 of a new kind of glass, the basis of which is the oxyd of 

 zinc, a certain quantity of boracic acid being added. Its 

 extreme limpidity, and total freedom from color, and, so 

 far as appears, from veins and striae, seem eminently 

 to fit it for optical purposes; but this glass has not 

 stood as yet sufficient time to determine its real value. 

 A prize medal was awarded to M. Maes at the London 

 Exposition. 



The establishment of M. Guinand, at Paris, is now 

 conducted by M. Feil, grandson of P. L. Guinand, and the 

 following are the prices at which he furnishes discs of 

 either crown or flint-glass of the first quality for tele- 

 scopes : 



4 inches diameter, 60 francs. 



5 " " 100 " 



6 " " 200 " 



7 250 " 



8 " " 400 " 



450 



10 inches diameter, 500 francs. 



11 " " 550 " 



12 " " 600 " 

 14 " " 1000 ' 

 16 " u 2000 " 

 20 " " 6000 " 



Mr. Joseph Baden, of Kohlgrub, in Bavaria, was for- 

 merly a workman in the establishment of Utschneider, 

 at Munich, but for many years has conducted an es- 



