150 Mr Pritchard on forming Diamonds 



feet diamond lens, and have at length succeeded in completing 

 a double convex of equal radii, of about ^^jth of an inch in fo- 

 cus, bearing an aperture of ^^ih of an inch with distinctness 

 on opaque objects, and its entire diameter on transparent ones. 

 It was finished at the conclusion of the year 1826. The date 

 of its final completion has by many been considered a remarka- 

 ble 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 Goring's Amician reflector, but with- 

 out 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 with the same angle of aperture. 

 The advantage of seeing an object without aberration by the in- 

 terposition of but a single magnifier, instead of looking at a pic- 

 ture of it (however perfect) with an eye-glass, must surely be 

 duly appreciated by every person endowed with ordinary rea- 

 son. 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 ar- 

 rangement whatever ; it is like seeing an action performed in- 

 stead of scenic representation of it, or being informed of its oc- 

 currence on the most indisputable and accurate testimony. 



Previous to grinding a diamond into a spherical figure it is 

 absolutely necessary tliat it should be ground flat and parallel 

 on both sides, (if not a larke 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 extremely 

 dangerous to commence the process of grinding, for many dia- 



* In Dr Brewster's Treatise on Neiv Philosophical Instruments, Book 

 V. chap. 2, page 403, Account of a new compound microscope for objects 

 of Natural History, is the following passage : — " We cannot, therefore, 

 expect any essential improvement in the single microscope, unless from the 

 discovery of some transparent substance which, like the diamond, com- 

 bines a high refractive with a low dispersive power." From which it 

 seems certain that the Doctor did not contemplate the possibility of work- 

 ing on the substance of the diamond, though he must have been aware 

 of its valuable properties. — A. P. 



