The Bed Admiral Butterfly, and the Lepisma Saccharina. 59 



and placed at a slight inclination downwards as well. It will thus 

 appear that the central portion of the lens is stopped out for the 

 direct rays, while a greater portion of light is admitted from one 

 side than the other, and being placed transversely to the edge of the 

 prism, or from C to D of Fig. 2, and with the larger space B, Fig. 3, 

 on the left-hand side, the bulk of the light is sent across towards 

 the prism and helps to compensate for the loss by reflexions within 

 it. By running the condenser up and down it will be seen that 

 the quality of the light varies very much in its different parts, and 

 by slightly turning the mirror to one or the other side the most 

 varied effects will be produced ; but at the edge where the effects of 

 diffraction would be found, the greatest distinctness will be seen to 

 occur. Then, again, the stop being of polished tin and slightly 

 inclined downwards, a portion of the refracted rays will probably be 

 reflected downwards by the plane side of the lens, and being met 

 by the reflecting surface of the tin, will be thrown upwards again, 

 helping to break the gloom of the otherwise darkened part of the 

 circle. In addition to this, there would seem to be a considerable 

 amount of light reflected downwards by the surface of the covering 

 glass or the under surface of the object lens, for objects thus 

 illumined have the appearance of being lighted up with both trans- 

 mitted and reflected light, so that the most delicate surface mark- 

 ings and the most transparent tissues become remarkably and most 

 beautifully distinct, and indeed I have never before seen the more 

 delicate membranes of Infusoria, Zoophytes, &c, brought out with 

 such exquisite delicacy and clearness. It should be observed that a 

 piece of finely-ground glass should be placed beneath the slide, and 

 with artificial light this glass should be of a pale neutral tint and 

 the ground side upwards, and only just sufficiently distant to be 

 quite out of the focus. 



VI. — On the Spherules which compose the Ribs of the Scales of 

 the Red Admiral Butterfly (Vanessa Atalanta), and the Lepisma 

 Saccharina. By G. W. Royston-Pigott, M.A., &c. 



The scales of this splendid insect exhibit by reflected light fine 

 shades of red, brown, and yellow. Some of them are intensely 

 black, resembling the dead black of the finest velvet. It is upon 

 these apparently black scales I now propose to make a few observa- 

 tions with a succession of object-glasses. 



1. By transmitted light with a low-angled " inch," the particular 

 scale now under notice is of a fine Indian-ink colour, approaching 

 burnt sienna ; daylight without sunshine. Under a fine half-inch 



VOL. IX. P 



