15 



On the Art of forming Diamonds into single Lenses for 



Microscopes. — By Mr. A. Pritchard. 



[Communicated by Dr. Goring.] 



Of the various improvements in Microscopes originated by 

 Dr. Goring, that which he conceives to be the most important 

 is the construction of single magnifiers from adamant. The 

 details relative to this novel class of instruments, I have been 

 induced to lay before the public. Single microscopes natu- 

 rally aplanatic, or at least sufficiently so for practical pur- 

 poses, possess an incontestable superiority over all others, and 

 must be recognised by the scientific as verging towards the 

 ultimatum of improvement in magnifying glasses. The ad* 

 vantages obtained by the most improved compound engi- 

 Bcopes over single microscopes resolve themselves into the at- 

 tainment of vision without aberration with considerable angles 

 of aperture; but against this must be set the never-to-be-forgot- 

 ten fact, that they only show us a picture of an object instead 

 of nature itself; now a Diamond Lens shows us our real 

 object without any sensible aberration like that produced by 

 glass lenses ; and we are entitled, I think, to expect new dis- 

 coveries in miscrosopic science, even at this late period, from 

 very deep single lenses of adamant*. I shall not fatigue my 



♦ It seems generally admitted that, within a certain range of power not 

 exceeding that of a lens of s'cth of an inch focus, the beauty and truth of 

 the vision given by the new compound microscopes cannot be equalled 

 by that of any single instrument, at least of glass. It is no less true, 

 however, that the picture of the compounds, however perfect, is not 

 like a real object, will not admit of amplification beyond a certain 

 point with advantage. Under the action of very deep eye-glasses, the 

 image of opaque objects especially, first loses its strong, well-deter- 

 mined outline— then grows soft and nebulous, and finally melts away in 

 shadowy confusion. Let the experiment be made of raising the power 

 of a compound up to that of a Jgth inch lens — then try it against the 

 single microscope of that power (having, of course, the utmost opening 

 the nature of the object viewed will permit). The observer, if open to 

 conviction, will soon be taught the superior efficacy of the latter — for it 

 will show the lines on the dust of Menelaus with such force and viva*- 

 city, that they will always be apparent without any particular manage^ 

 merit of the light— nor can their image be extinguished by causing the 

 illumination to be directed truly through the axis of the lens (as it al- 

 uays may in the compounds), A due consideration of the teeth and 

 inequalities on the surface of a human hair, together with the transverse 



