Dr Goring on Monochromatic Light, §c. 67 



Reflexion of Light" in the construction of this instrument; 

 and if he had succeeded in making it achromatic, there would 

 be good reason for asserting that it is unnecessary to correct 

 the dispersion of its object-glass separately, as well as " that the 

 intellectual and manual labour, which has of late years been 

 expended on the construction of achromatic object-glasses, has 

 not only been unprofitable directed," but in a manner wholly 

 thrown away, since, if his theories were accurate, a much bet- 

 ter and purer achromatism ought to be obtained by the simple 

 adjustment of a system of lenses to proper intervals. I assert 

 point blank, that his instrument is as complete a failure as any 

 thing of the sort I ever attempted myself. I have examined 

 one of these instruments of the latest and most improved con- 

 struction, made by Mr Carey, (which, however, differed not 

 materially from that described in the treatise on Optical In- 

 struments, except in having a double field-glass,)* and can, I 

 think, be positive that both the chromatic and spherical aber- 

 ration of the objective part was wholly untouched, and that the 

 eye-piece, consisting of four glasses, was achromatic. Nothing 

 can surpass the beauty of the field of this microscope ; but if I 

 may be allowed the expression, notwithstanding its extent and 

 flatness, nothing more can be made to grow in it than in that 

 of any ordinary compound microscope having a well figured 

 object-glass of the same power, and angular aperture, used 

 with an Huygenian eye-piece, also of equal power with that 

 applied to the instrument in question. 



The dispersive and spherical error of small lenses is un- 

 doubtedly small, as I have frequently remarked ; but it is not 

 insensible even with a very small aperture to those who know 

 how and where to look for it. Some persons use it at the first 

 glance, others only if it is pointed out to them, and some not 

 at all, if it happens to contradict their theories and precon- 

 ceived opinions ; for there is no blindness greater than that ge- 

 nerated, not in the organ of sight itself, but in the mind which re- 

 ceives its impressions. We are indeed so accustomed to tolerate 

 aberration in microscopes that it frequently is unable to sti- 

 mulate our senses. I shall here instruct my reader, if I can, 



Thii w.i- iniilai to that described in No 5, Ait. xvji, p. l5&of this 

 Journal. 



