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flDicroecopical Jtiiaoer?. 



By Dr. Royston-Pigott, M.A., F.R.S. 



Plate XX. Part 3. 



Brilliant Miniatures and Minute Molecules, 

 colias cosonia. 



ATURE produces no more splendid phenomena 

 than those of a minute solar beam of light as 

 emitted by the heliostat alluded to in the last article. 

 A small plano-convex lens is attached to the 

 sub-stage and centred accurately. The microscope 

 focusses on the solar image. In beauty of form, 

 accuracy of tracery, variety of patterns, and solar 

 glory of colouring, nothing in Nature rivals these 

 phenomena. Their splendour overpowers the 

 observer, who to escape injury hurriedly seizes on any known 

 methods of subduing their intolerable brilliance. ^Smaller and 

 smaller beams were employed, a lengthened tube, and deeper 

 eyepieces, until the spectacle became bearable. They were then 

 copied so faithfully by a deaf-and-dumb artist as to elicit admira- 

 tion at a meeting of the Royal Society. A sunlit room assisted 

 their deUneation. A very slight obliquity or excentricity of the 

 stage-lens developed strange transformations from circular to 

 conical curves. 



So soon as the convex lens regains its true axial position, all 

 these figures become circular. When the focus is changed 

 slightly, the rings either expand or contract. The simple lens 

 being naturally " uncorrected," presents these rings below the best 

 focus ; whilst above it they resolve into the mist or fog of spherical 

 aberration. If a miniaturing objective be now substituted for the 

 little stage-lens, these rings, by properly adjusting the screw- 

 collars, may be produced on both sides of the best focus — i.e.^ 

 beyond it and above it — of very similar appearance. Seen only 

 above it, they denote over correction ; seen only below it, they 

 denote under-correction. 

 Journal of Microscopy and Natural Scirnce, 



New Series. Vol. II. i88q. s 



