22 MICROSCOPIC OBJECTS. 



and indeed all other constructions of the compound, was 

 manifest. It may be remarked, that Dr. Goring had 

 tried Euler's proposal of reducing the aberrations by 

 combining two plano-convex lenses for the object-glass, 

 and also Herschel's combinations for producing a mini- 

 mum of aberrations, from his investigations pubhshed 

 in the Philosophical Transactions for 1821. 



About the same time (1825) Mr, Lister procured an 

 achromatic microscope from Paris, and placed it in the 

 hands of Dr. Goring for trial. Both these gentlemen 

 w^ere at first disappointed with the performance of this 

 instrument; but when Dr. Goring had increased the 

 angle-of-aperture of the object-glasses, by enlarging the 

 small diaphragm or stop behind them, the performance 

 was greatly improved, and its achromatism (which, 

 owing to the thinness of the pairs of lenses, had been 

 doubted,) clearly established. 



These improvements were communicated to the 

 scientific world in the Journal of the Royal Institution ; 

 and in 1829, Dr. Goring gave the public a practical and 

 detailed account of the results in the 'Microscopic 

 Illustrations.' * All subsequent improvements in the 

 achromatic microscope are merely further developments 

 of the same plan, or, in other words, further progress 

 along the same road. 



It may now be proper to offer to the reader a few 



* A Third Edition of this work, with a Supplement, has been 

 published since Dr. Goriog's death. 



