258 



Dn Goring's Commentary on 



advertised for exhibition to the whole world, and has been 

 examined, and highly approved of, by many sufficient judges; 

 he has, moreover, a diamond now in his possession which he 

 intends to form into a lens, which, in its flat state, shewed no 

 traces of double refraction or polarization. Before I caused 

 the first diamond lens to be worked, Messrs. Rundell and 

 Bridge were so polite as to allow me to examine several of 

 their Asiatic laske or plate diamonds, one of which I saw 

 through as if it had been a piece of common glass. 



It is much to be regretted that the difficulty of procuring 

 rough diamonds in this country, together with the vast expense 

 connected with all operations on them, has not yet permitted 

 us to ascertain that particular form or forms of crystallization 

 in the diamond, which denote its fitness for optical purposes; 

 this, however, will no doubt be discovered hereafter. Now, if 

 it is admitted that some diamonds can be procui;ed free from 

 flaws, crystallized texture, and polarization , or that the 

 double refraction of others can be subdued, it seems to me 

 impossible to deny, that of all the substances furnished 

 either by nature or art, adamant is, upon the whole, that best 

 adapted for making small lenses, on account of its freedom 



" radii for parallel rays, and the numerical coefficient of the least aberration, ap- 

 *' proximately in some cases, but with sufficient accuracy for most purposes." 



