HISTORY OF THE MICROSCOPE. 13 



to be taken as a basis for the microscopic object-glass : it 

 diminishes very nearly half the loss of light from reflec- 

 tion, which is considerable at the numerous surfaces of a 

 combination ; the clearness of the field and brightness of 

 the picture is evidently increased by doing this; and it 

 prevents any dewiness or vegetation from forming on the 

 inner surfaces. Since this time, Mr. Eoss has been con- 

 stantly employed in bringing the manufacture of object- 

 glasses to their greatest perfection, and at length they 

 have attained to their present improved manufacture. 

 Having applied Mr. Lister's principles with a degree of 

 success never anticipated, so perfect were the corrections 

 given to the achromatic object-glass, so completely were 

 the errors of sphericity and dispersion balanced or de- 

 stroyed, that the circumstance of covering the object 

 with a plate of the thinnest glass or talc disturbed the 

 corrections, if they had been adapted to an uncovered 

 object, and rendered an object-glass which was perfect 

 under one condition sensibly defective under the other. 

 Here was another and unexpected difficulty to be over- 

 come, but which was finally accomplished; for in a com- 

 munication made to the Society of Arts in 1837, Mr. Ross 

 stated, that by separating the anterior lens in the combi- 

 nation from the other two, he had been completely suc- 

 cessful. The construction of this object-glass will be 

 illustrated and explained in a future chapter. 



The rapid improvement in the manufacture of the 

 achromatic compound microscope in this country has been 

 greatly furthered by the spirit of liberality evinced by Sir 

 David Brewster, the late Dr. Goring, Mr. R. H. Solly, 

 and Mr. Bowerbank. To the patronage of Dr. Goring 

 we owe the construction of the first triplet achromatic 

 object-glass, of the diamond lens, and of the improved 

 reflecting instrument of Amici by Cuthbert. 



The achromatic microscopes now manufactured by our 

 London makers, Mr. Ross, Messrs. Powell and Lealand, 

 and Messrs. Smith and Beck, are unequalled in any part 

 of the world. This opinion is confirmed by the reports of 

 the juries on the Exhibition of Works of Industry of all 

 Nations, 1851; at that time the instruments exhibited by 

 Mr. Ross and Messrs. Smith and Beck, by far excelled 



