18 Mr. Pritchard on Diamond 



the interposition of but a single magnifier, instead of looking 

 at a picture of it (however perfect) with an eye-glass, must 

 surely be duly appreciated by every person endowed with 

 ordinary reason. It requires little knowledge of optics to be 

 convinced that the simple unadulterated view of an object must 

 enable us to look farther into its real texture, than we can see 

 by any artificial arrangement whatever ; it is like seeing an 

 action performed instead of a scenic representation of it, or 

 being informed of its occurrence by the most indisputable and 

 accurate testimony. 



Previous to grinding a diamond into a spherical figure, it is 

 absolutely necessary that it should be ground flat, and parallel 

 on both sides (if not a Laske or plate diamond), so that we 

 may be enabled to see through it, and try it as opticians try a 

 piece of flint glass : without this preparatory step, it will be ex- 

 tremely dangerous to commence the process of grinding, for 

 many diamonds give a double, or even a species of triple refrac- 

 tion, forming two or three images of an object ; this polariza- 

 tion of the light, arising from the primitive form of the crystal, 

 of course totally unfits them for making lenses*. I need not 

 observe, that it must he chosen of the finest water, and free 

 from all visible flaws when examined by a deep magnifier. It 

 was extremely fortunate for diamond lenses that the first made 

 was free from the defect of double vision, otherwise diamonds 

 en masse might at once have been abandoned as unfit for opti- 

 cal purposes. The cause why some stones give single vision, 

 and others several peculiar refractions, may also arise from 

 different degrees of density or hardness occurring in the same 

 stone. Diamond-cutters are in the habit of designating stones 

 male and female, sometimes a he and she (as they have it) 

 are united in the same gem, — their he means merely a hard 

 stone, and their she a soft one. When a diamond which will 

 give several refractions is ground into a spherical figure and 

 partially polished, it is seen by the microscope to exhibit a 



* There are fourteen different crystalline forms of the diamond, and of 

 this number, from the laws which govern the polarization of light, the 

 octohedron and truncated cube are probably the only ones that will give 

 single vision. It is unfortunately very difficult to procure rough dia- 

 monds in this coimtry, so we are compelled to use stones already cut, 

 and to subject them to trial in the way mentioned in the text. 



