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XIII. On some properties in achromatic object-glasses applicable to the improve- 
ment of the microscope. By Joseph Jackson Lister, Esq. Communicated by 
Dr. Roget, Secretary. 
Read January 21, 1830. 
The improvement of the achromatic compound miscroscope 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 microscope which have originated apparently indepen- 
dent of each other within a few years past. 
The first produced in England were the triple ones constructed in 1824 and 
] 825 by Tulley, who had been incited to the undertaking by Dr. Goring : 
of these an account is already before the public. Tulley has since adopted 
for his triple object-glass to be used singly the focal length of 0.9 inch, apply- 
ing 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 perfec- 
tion. His first glasses have all the merit of a new invention, having been 
executed without the knowledge that any thing of the kind previously existed, 
though other achromatic glasses had before been made in France by Selligue, 
by Fraunhofer at Munich, and by Amici at Modena. 
The glasses of Selligue’s microscope, of which a report was made by 
M. Fresnel 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 cemented together. Four of these, of from If to If inch 
2 b 2 
