20 MICROSCOPIC OBJECTS. 



form of, and the refrangibility produced by, the object- 

 glass. This invention constituted a new era in astronomical 

 science. Indeed so great was the progress of astronomy 

 in consequence, that the question would naturally suggest 

 itself, " Why do not opticians apply the achromatic 

 construction to the microscope ? Surely similar results 

 in other sciences might be expected." Whereas it was 

 not effectively appHed to the microscope until the year 

 1824. This enigma it is now proposed to solve. 



Soon after the achromatic telescope was perfected, 

 Benjamin Martin and others actually made achromatic 

 object-glasses for microscopes ; but these lenses failed 

 to produce any improvement. Similar trials were made, 

 and results obtained, from that time to the year 1815, 

 when Professor Amici, then of Modena, pubhshed an 

 account of his improvements in microscopes. These 

 improvements were made both on the refracting and 

 reflecting kinds ; the former of which he made 

 achromatic : he then abandoned it, and devoted his 

 superior talents to perfecting the reflecting microscope. 

 This is sufficient to show the relative estimation in which 

 he held those constructions. About the year 1824, 

 MM. Selligue and Vincent and Charles Chevaher, 

 in France, constructed achromatic microscopes. One of 

 these instruments, by the latter artist, was sent to 

 England, and was examined by a celebrated optician 

 here, who stated that it was of first-rate workmanship, 

 but in performance did not surpass that of a good com- 

 pound microscope when well made. In the same year. 



