Mr Lister on Achromatic compound Microscopes. 249 



always be tried and executed on this scale, which would not 

 strain the powers of a real artist too much. 



The principal opticians in Europe have made achromatic 

 object-glasses for engyscopes for some years, and are immea- 

 surably in advance of the mathematicians on this subject. If 

 the latter gentlemen do not choose to turn their attention to 

 it, I presume they will be content to retire into the shade ; to 

 abate somewhat of their magnificent pretensions to infallibility 

 and exactitude ; and to admit that for once analysis has been 

 beaten by experiment, at least in the pitiful, pimping, insig- 

 nificant, article of the object-glass of a compound microscope, 

 which being such a mere trifle cannot of course I'enect any dis- 

 grace on their incapacity to handle it. 



-" tractata quaeque nitescere posse 



" Desperant, relinquunt."- 

 Lambeth, June 30, 1831. 



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

 applicable to the improvement of the Microscope. By Jo- 

 seph Jackson Lister, Esq- (Concluded from No. ix. page 

 180.) 



\Jv several purposes to which the particulars just given seem 

 applicable, I must at present confine myself to the most ob- 

 vious one. They furnish the means of destroying with the 

 utmost case both aberrations in a large focal pencil, and of thus 

 surmounting what has been hitherto the chief obstacle to the 

 perfection of the microscope. And when it is considered that 

 the curves of its diminutive object-glasses have required to be 

 at least as exactly proportioned as those of a large telescope, 

 to jrivc the image of a bright point equally sharp and colour- 

 less, and that any change made to correct one aberration was 

 liable to disturb the other, some idea may be formed of what 

 the amount of that obstacle must have been. It will however 

 be evident, that if any object-glass is but made achromatic, 

 with its lenses truly worked and cemented so that their axes 

 coincide, it may with certainty be connected with another pos- 

 sessing the same requisites and of suitable focus, so that tin 



