Jjelfasi Mi.iurul History t^ocitUj. 3SJI 



»3very operation^ that he might be able to repeat any experi- 

 ment which might chance to be successful. At length ho 

 obtained blocks of glass which contained portions perfectly 

 homogeneous; these he separated by sawing the blocks into 

 sections, selecting those parts which were free from defects, 

 and returning the others to the crucible. Afterwards he im- 

 proved upon this process by casting his glass in moiilds* 

 The refraction of M. Guinand's gla'^s varies almost at every 

 casting; but at each casting the whole mass is so perfectly 

 homogeneous^ that two portions, taken indifferently from the 

 top and bottom of the crucible, have the same refractive 

 « power. 



M Guinand obtained such reputation by the manufacture 

 of achromatic telescopes from his glass, that he was visited by 

 many scientific men of different parts of Europe ; and in 

 1805, was called into Bavaria, 2.60 miles from his home, in 

 the employment of M Frauenhofer, a celebrated optician. 

 Here he continued nin'e years occupied almost solely in the 

 manufacture of glass ; and it is from this period that M. 

 Fraut-nhofer's achromatic telescopes have acquired so well- 

 merited a reputation. After returning from Bavaria to his 

 native country, he raised his discovery to a higher degree of 

 improvement; and in the last years of his life, succeeded 

 jn manufacturing disks of eleven and twelve inches of Eng- 

 lish measure, perfectly homogeneous, and free from defects* 



The pecuniary circumstances of M. Guinand prevented 

 his divulging the process for manufacturing his glass j 

 arrangements had been made by the French government for 

 purchasing the secret, when the artist, verging on his 80lh 

 year, died after a short illness. His son remains in posses- 

 sion of the process, ;)nd it is to be hoped that an improvement 

 which opens the way to such important acquisitions in the field 

 of astronomy will not be lost. C H. 



1 8. Belfast Natural History Society. — The Society insti- 

 tuted in Belfast, Ireland, for the cultivation of Natural His- 

 tory, and mentioned by Mr. Maclure in his letters contained 

 in the last number of our Journal, consists, as he informs us, 

 of active intelligent young men, and from this circumstance, 

 as well as from its location in the vicinity of the celebrated 

 Giant's Causeway, we may look for interesting results from 

 »ts labours. Bv the recommendation of Mr. Maclure, the 



