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Art. XVI. Miscellaneous Intelligeme. 



I. Mechanical Science. 

 S 1. Agbiculture, Optics, Astronomy, &c. 



1 , Apparatus for ihewing the double Refraction of Minerals, — 

 In the Journal of Science, Vol. X., p. 168, two methods of find- 

 ing the double refraction of minerals have been quoted from M. 

 Soret, in the Journal de Physique, Tom. XC, p. 353 ; and lest 

 the public should be led by that notice to ascribe the invention 

 of them to him, M. Soret has thought it of sufficient importance 

 to declare, in a letter to the editor, " That the apparatus are 

 not of his invention, but belong to M. Biot." 



M. Soret must certainly have misunderstood M. Biot, for he 

 has undoubtedly no claim whatever to the invention of these two 

 kinds of apparatus. Dr. Brewster was the first person who em- 

 ployed the apparatus of two plates of a singly refracting crystal, 

 placed transversely : the crystal which he used was Agate. A 

 long time afterwards M. Biot discovered an analogous property 

 in the Tourmaline, and substituted it in place of the agate, but 

 the apparatus did not on this account become of his invention. 

 Dr. Brewster was also the first who used Agate Microscopes, 

 consisting chiefly of thin plates cemented on plano-convex lenses, 

 and he has since constructed similar apparatus by converting 

 calcareous spar and artificial salts into singly-refracting plates, 

 (See Philosophical Transactions, 1819, p. 149,) and has also re- 

 peatedly used analogous apparatus, consisting of transverse 

 parcels of films of glass blown to extreme thinness, and films 

 of mica arranged in a particular manner. The merit which 

 belongs to M. Biot is that of having discovered that Tourma' 

 line has the singly refracting and polarising property of 

 Agate. 



M. Soret must have ascribed the second apparatus to M. Biot, 

 solely because he had exhibited to him the experiment. It belongs 

 exclusively to Dr. Brewster, who shewed the experiments to 

 Major Petersen in 1816 and 1817, and to Count Breunner, and 

 Professor Mohs in 1818. (See the Philosophical Transactions^ 

 1819, p. 11., and the Journal de Physique, Mars, 1820, Tom. 

 XC, p. 177, the same volume in which M. Soret ascribes the 

 invention toM. Biot.) 



