208 MICROSCOPICAL IMAGERY. 



But the glass must be exceptionally good, and the condenser free 

 from aberration, as in a good objective h or J-inch. Daylight 

 succeeds the best. 



The molecules composing the co7'07iefs are finer than those of the 

 clothes-moth scale (Tinea vest). I first discerned the remarkable 

 rippling on the scales of Colias with a fine Hinton * J-inch objec- 

 tive, price ;£i 5s. Very few glasses of that power will render 

 anything visible, but an irregular, dim, misty, and ill-defined 

 mottling. I have found green Dammar a good mounting medium, 

 or they can be seen mounted dry. 



The molecules forming beautifully minute circlets, enclosing a 

 central bright disc, are still smaller, and try the objective quality 

 severely. Their colour is a very deep violet. Chatelains, beaded 

 bars, parallel rows, wavy depositions, and irregular groups, princi- 

 pally distinguish these scales. An immersion condenser of large 

 aperture with direct central daylight, strongly illuminated the field. 

 Perforated mahogany slips mounted with two glass covers allow 

 the condenser to make oil contact with the lower cover, which is 

 I — 60th thick. 



The central engraving in the plate represents the dust 

 off a huge Indian Moth, yet one which exhibits almost the 

 smallest molecules known, excepting those of Colias CcBso?iia. 

 They display black test-rings of great beauty, as well as brilliant 

 focal discs adorned with chromatic tints. Their exceedingly close 

 packings in masses of strata greatly increases the difficulty of their 

 resolution. On shewing it to one of the best London microsco- 

 pists, he declared it was the most wonderful resolution he had ever 

 seen. The Colias possesses indeed much smaller molecules ; but 

 as they are tolerably sparse, they can be quite well seen with a 

 very high-class apochromatic, i — 12th oil immersion. 



Description of Plate. 



The figures in the plate can be developed in an undarkened 



room with amazing splendour, notwithstanding full sunshine. 



All the figures, at a power of 1,000 diameters, were seen with a 



fine Powell and Lcaland ^th immersion. Fig. V. shows the 



* Mr. Hinton (Vorley Road, HoUoway) also supplies Colias Ccesonia, 

 beautifully mounted. 



