Lenses for Microscopes, 17 



figure, and examined by Mr. Levi, who expressed great 

 astonishment at it, and added that he was not acquainted with 

 any means by which that ligure could have been effected : 

 unfortunately this stone was irrecoverably lost. Mr. Varley 

 having returned from the country, becoming now thoroughly 

 heated with the project, permitted me to complete another 

 diamond, which had been presented to me by Dr. G. : this 

 is a plano-convex of about ihe^^jth of an inch focus : it was 

 not thought advisable to polish it more than sufficed to enable 

 us to see objects through it, because several flaws, before 

 invisible, made their appearance in the process of polishing. 

 In spite of all its imperfections, it plainly convinced us of the 

 superiority which a perfect diamond lens would possess by its 

 style of performance, both as a single magnifier and as the 

 object lens of a compound microscope. After the completion 

 of my articles with Mr. V., being entirely under my own com- 

 mand, I devoted some time to the formation of a perfect 

 diamond lens, and have at length succeeded in completing a 

 double convex of equal radii of about ^th of an inch focus, 

 bearing an aperture of ^yh of an inch with distinctness on 

 opaque objects, and its entire diameter on transparent ones ; 

 it was finished at the conclusion of last year. The date of its 

 final completion has by many been considered a remarkable 

 epoch in the history of the microscope, being the first perfect 

 one ever made or thought of in any part of the world*. I think 

 it sufficient to say of this adamantine lens that it gives vision 

 with a trifling chromatic aberration, but in other respects 

 exceedingly like that of Dr. G.'s Amician reflector, but 

 without its darkness: for it is quite evident that its light 

 must be superior to that of any compound microscope whatever, 

 acting with the same power and the same angle of aperture. 

 The advantage of seeing an object without aberration by 



* In Dr. Brewster's treatise on new Philosophical instruments, Book 5, 

 chan. 2, Pag^e 403— Account of a new compound Microscope for objects 

 of Natural History — is the followinjr passage : *' We cannot therefore ex- 

 *' pect any essential improvement in the single microscope, unless from 

 I* the discovery of some transparent substance, which like the diamond 

 *' combines a high refractive with a low dispersive power." From which 

 it seems certain that the Doctor never contemplated the possibility of 

 working upon the substance of the diamond, though he must have been 

 aware of its valuable properties. 



JULY— OCT. 1827. C 



