1886.] 



MICROSCOPICAL JOURNAL. 



29 



many years of observation of this ob- 

 ject, this result is perfectly startling, 

 and throws a strong doubt vipon 

 innumerable accepted appearances. 

 The black boundary edges are very 

 nearly 1-100,000 thick. 



The hair of English bat also exhib- 

 its tests of a very high order. 

 Pritchard's plate represents it as 

 tufted with black appendages, 

 through which a transparent tube is 

 carried. The complete resolution of 

 these tufts show that there are inter- 

 nal tubules somewhat spirally ar- 

 ranged in great profusion, the edges 

 of which are marked very strongly 

 black, with sudden interruptions. A 

 more intense scrutiny reveals these 

 tubes filled mostly with brilliant 

 molecules var3'ing from the i -So. 000 

 to the 1-120,000 of an inch in diame- 

 ter. 



A very charming phenomenon is 

 seen when one stringlet of beads 

 _ partly overlaps another deeper set. 

 As no light can pass through the 

 spherules at the overlaps, intense 

 blackness takes a varietv of forms. 

 The beads are not all quite spherular ; 

 some are ovoid ; solitary beads are 

 obsei-\'able, occurring in straight or 

 curved clusters of two, three, or 

 more, or in long chains. If an 

 upper chain is brilliant with focal 

 light, a lower set is often dark. As 

 many as a dozen stringlets often ap- 

 pear packed at one place in different 

 bunches or fagots, and, of course, 

 lying in several different focal 

 planes ; and if the glass be trascend- 

 ently fine, these spherules glitter 

 with a variety of focal colors of 

 great beauty. Pale turquoise and 

 ruby color, with shades of orange 

 yellow and pale yellow approaching 

 white. 



Advancing- Ang'ular Apert?irc. — 

 As already described, a constant ef- 

 fect of small angular aperture is to 

 darken organic structure. Black 

 margins of cylinders, tubes, and 

 spherules are made darker and 

 broader. This black margin obeys a 

 mathematical law. Its breadth va- 



ries as the refractive index increases, 

 and as the aperture diminishes. 



If the same power be attained, 

 either with deeper eve-pieces and 

 weak objectives, as contrasted with 

 shallow eye-pieces and deep objec- 

 tives, the difierence in the appear- 

 ances is very striking and instructive. 

 Here is a beatiful example — Airo- 

 pos Achero9itia (Death's Head 

 Moth) . Change of angular aperture 

 gives startling results. The whole 

 animal bristles with a forest of spear- 

 lets of exceeding sharpness, each 

 feather having three or four long 

 spines. 



With low aperture the scales pre- 

 sent a superbly rich and dark amber- 

 brown color by transmitted light. 

 Tipped with a black point, a thin 

 line of light runs up the spear edged 

 with fine black borders. It will be 

 probably admitted that the black an- 

 nuli,or rings, of each spherule, if they 

 exist in this scale, are too deep and 

 broad under a low aperture to per- 

 mit any visible streamlets of light to 

 escape through them, so as to efiect- 

 ively impress their existence upon the 

 retina of the observer. Beads appear 

 dark till sufficiently magnified and 

 illuminated. 



But as objectives and eye-pieces are 

 used of the same power as before un- 

 der wider angular aperture of objec- 

 tive vision, this deep brown color 

 pales. The universal molecular sys- 

 tem of which the scale is composed 

 begins to light up and glisten ; each 

 spherule obeys the law emuiciated ; 

 its annulus narrows ; the light per- 

 meates the scale profusely. The 

 general effect is to change dark into 

 brighter tints. Enlarged aperture 

 now enables a sparkling radiance to 

 steal through the featherlet. As 

 power is increased, masses of or- 

 ganic molecules, as yet invisible, con- 

 tribute streaks and mottlings of pris- 

 matic colorings. And now, if high 

 power and large aperture, with su- 

 pei'b definition, be emploved, a new 

 vision of beauty and refinement 

 bursts upon the eye. The scale glit- 



