of the Red Admiral Butterfly, and the Lepisma Saccharina. 65 



It has been roundly stated that, when strise intersect, spurious 

 beads are produced or seen at their intersections. And that this is 

 especially the case with the crossing strise of the Lepisma. 



To this I reply, a finer glass dissipates these ghost beads 

 entirely, and replaces them by others very much smaller and at 

 least ten times more numerous. These ghost beads demonstrate 

 (not the existence of the smaller reality but) the absurd correction 

 and errors of the microscope itself. 



The lovers of these ghosts may stick to their spurious showings 

 and prefer them, whilst a wealth of fascinating beauty lies hid from 

 their gaze. Residuary aberration still hovers about our best 

 glasses. Perfect achromatism and perfect correction of spherical 

 aberration are at present almost incongruous. Correct the one, 

 then the other appears. Get rid of the colour totally and you will 

 see woolly and blurred outlines, thick edges, and spurious beads or 

 ghosts. What is the pleasure or advantage of seeing for instance 

 say forty spurious beads in the Lepisma, when these forty should 

 vanish and make room for four hundred realities — rows upon rows 

 of tiny, shiny gems instead of a few non-existent spurious images ? 

 The intercostal spaces of the Lepisma, like the Podura curvi- 

 collis, teem with closely-packed rows of beading: admirers of 

 Podura nails can see nothing in the blank spaces : and champions of 

 the Lepisma ghosts can see nothing there between the ribs, but 

 ghostly shams of intersecting striae. In each, these blank spaces 

 are full ; but not till the aberrating obnoxious rays are controlled 

 can these tiny strings of pearls start into view. A greenish-blue 

 sky above a setting sun, for instance, gives comparatively few 

 aberrating rays in my l-50th immersion. The more colours the 

 light contains, the more difficult becomes the destruction of the 

 aberration. The finest effects in Colonel Woodward's photography 

 could only be produced when the number of the colours was reduced 

 to the blue ray which now alone exactly suits his photography. But 

 we use all mixed together in our daily researches, and involve our- 

 selves in the mists of residuary aberration. 



It is when the ribs appear sharj>er, thinner, and the intercostal 

 spaces become broader ; when sharp, keen black lines take the place 

 of blurred thick outlines; when the quill is keenly portrayed and 

 the serrations finely pronounced, — it is then only that the aberration 

 approaches a minimum, and then that we may expect to see with a 

 little obliquity of light the gratifying sight of that inner structure 

 which has hitherto eluded the eyes of the most diligent micro- 

 scopists of modern times. 



