16 Mr. Pritchard on Diamond 



readers by describing the difficulties which were encountered 

 in the prosecution of the design of making diamond lenses. 

 Nature does not seem to permit us to produce any thing of 

 surpassing excellence without proportional effort, and I shall 

 simply say, that in its infancy the project of grinding and 

 polishing the refractory substance of Adamant was far more 

 hopeless than that of making achromatic glass lenses of 0.2 of 

 an inch focus. I conceive it just to state that Messrs. Rundell 

 and Bridge, of Ludgate-hill, had, at the time of the com- 

 mencement of my labours, many Dutch diamond cutters at 

 work, and that the foreman, Mr. Levi, with all his men, assured 

 me, that it was impossible to work diamonds into spherical 

 curves ; the same opinion was also expressed by several others 

 who were considered of standard authority in such matters. 



Notwithstanding this discouragement, in the summer of 

 the year 1824, I was instigated by Dr. Goring (at his ex- 

 pense) to undertake the task of working a diamond lens ; 

 (being then under the tuition of Mr. C. Varley, who was 

 however at that time absent.) For this purpose, Dr. G, 

 forwarded to me a brilliant diamond, which, contrary to the 

 expectation of many, was at length ground into a spherical 



connecting fibres between the lines on the scales of the curculio imperialism 

 viewed as opaque objects, will suffice to complete the illustration of the 

 subject ; though the last object is not to be well seen by that kind of light 

 which is given by silver cups — and a single lens of e^gth inch focus can 

 of course have no other. The effectiveness and penetrating faculties of 

 simple magnifiers are invariably increased by an accession of power 

 however great — that of compounds seems to be deteriorated beyond cer- 

 tain limits. An opinion may be hazarded that the achromatics and reflec- 

 tors yet made do not really surpass the efficacy of equivalent single lenses ^ 

 even of glass, when their power exceeds that of a 5^0 th lens, from 201th to 

 4'oth the vision may be about equal — but from ^'oth upwards infinitely 

 inferior. 



The superior light of the single refraction can need no comment — and 

 it is evident that there must be a degree of power at which that of the 

 compounds will become too dim and feeble for vision, — while that of the 

 single instrument will still retain a due intensity. For these reasons it 

 is conceived that the close and penetrating scrutiny of lenses of diamond 

 of perhaps only the ^ioth inch focus, and an equal aperture (which their 

 very low aberration would easily admit of,) must enable us to see further 

 into the arcana of nature than we have yet been empowered to do. Glass 

 globules of 5U(jth inch focus and indeed much deeper have been executed ; 

 but the testimony of lenses of diamond would certainly be far more re- 

 spectable, and is at least worthy of trial and examination. — C. R. G. 



