iselfasi Natural History Society. 3et 
every operation, that he might be able to repeat any experi- 
ment which might chance to successful. At length he 
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- 
roved upon this process by casting bis glass in moulds, 
he refraction of M. Guinand’s gla-s varies almost at every 
casting; bul at each casting the whole mass is so perfectly 
_ homogeneous, that two portions, taken indifferently from the 
and bottom of the crucible, have the same refractive 
nand obtained such reputation by the manufacture 
the employment of M. Frauenhofer, a celebrated optician. 
ere he continued pine years occupied almost solely in the 
manufacture of glass; and it is from this period that M. 
Frauenhofer’s achromatic telescopes have acquired so well- 
merited a reputation. After returning from Bavaria to his _ 
native country, he raised his discovery to 4 higher degree of 
improvement; and in the tast years of his life, succeeded 
in manufacturing disks of eleven and twelve inches of Eng- 
lish measure, perfectly homogeneous, and free from defects. 
The pecuniary circumstances of M. Guinand prevented 
or 
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of active intelligent young men, an from this circumstance, 
as well as from its location in the vicinity of the celebrated 
Giani’s Causeway, we may look for interesting results from 
its labours. By the recommendation of Mr. Maclure, the 
