INTRODUCTORY REMARKS. / 



lens, that a skilful artist found but comparatively little 

 difficulty in succeeding. For, look at the loss of time 

 which must of necessity be incurred in making trial of 

 an achromatic. Every time each lens has to be tried, it 

 must be removed from its holder, the cement cleared off, 

 and then placed in its setting; whereas a metal is 

 always ready ; and there are no refractive or dispersive 

 powers to be ascertained, as with lenses, so that the 

 Amician reflecting microscopes were soon brought to 

 their most perfect condition. They have been made 

 with an angular aperture of 55 degrees, greatly surpassing 

 all the achromatics of that time. 



The improved Amician microscope soon became a 

 decided favourite with amateurs, and had it not been that 

 considerable tact and experience were required in 

 bringing out " its mettle, and that its range of effective 

 powers was limited, it would never, perhaps, have been 

 driven out of the field by our present achromatic micro- 

 scopes. I was soon convinced that of the three instru- 

 mentsthe Jewel-doublet, the Amician reflector, and 

 the Achromatic the latter would ultimately come into 

 general use. And entertaining this view of the subject, 

 I published, in conjunction with Dr. Goring, a very fiill 

 account of the method by which an artist may test the 

 value of his productions, and know whether or not he is 

 proceeding in the right path 5 for I conceive that it is of 

 no trivial import to have the causes of defects pointed 

 out, when we desire to correct them. Since this publica- 

 tion in the Microscopic Cabinet, other artists besides the 



