Mr Lister on the achromatic compound Microscope. 1G1) 



Art. XX. — On some properties in Achromatic Object-glasses 

 applicable to the improvement of the Microscope. By Jo- 

 seph Jackson Lister, Esq. 



The improvement of the achromatic compound microscope 

 having been an occasional object of my leisure for several years 

 past, my attention has in consequence been attracted to some 

 properties of object-glasses of short focus and large aperture, 

 which, so far as I am aware, have not been before noticed, and 

 which, I flatter myself, may be applied to increase its powers 

 and the ease of its manufacture. 



In offering these, accompanied by some other miscellaneous 

 remarks, it may be explanatory to introduce them by a short 

 notice of the several achromatic object-glasses for the micro- 

 scope which have originated apparently independent of each 

 other within a few years past. 



The first produced in England were the triple ones con- 

 structed in 1824 and 1825 by Tulley, who had been incited 

 to the undertaking by Dr Goring : of these an account is al- 

 ready before the public. Tulley has since adopted for his 

 triple object-glass to be used singly the focal length of 0.9 inch, 

 applying another of not quite 0.5 inch focus before it when 

 high magnifying power is required ; and he obtains with these 

 an image of great sharpness and perfection. His first glasses 

 have all the merit of a new invention, having been executed 

 without the knowledge that anything of the kind previously 

 existed, though other achromatic glasses had before been made 

 in France bv Selligue, by Fraunhofer at Munich, and by 

 Amici at Modena. 



The glasses of Selligue 1 s microscope, of which a report was 

 made by M. Fresncl to the Royal Academy of Sciences in 

 1824, were composed of a plano-concave lens of flint-glass, and 

 a double convex of crown or plate, with their inner curves ce- 

 mented together. Four of these, of from 1 ~ to 1 \ inch each 

 in focal length, were made to screw before each other, so as to 

 be used together or alone in the manner long practised with 

 single lenses. 



The chromatic aberration was thus in a considerable degrei 



