38 
BecK; on a new kind of Illumination. 
expanded by pressing the head between the forceps is very 
remarkable, so much so indeed that I made a rough sketch 
of the appearances, which are nevertheless perfectly unintel- 
ligible to me_, unless we have here an entire reversion of the 
correct appearance, or that those parts which appear light 
should be dark. The definition, however, with this object is 
perfect, and the deceptive appearances 'must be due to our 
not understanding the illumination. I have seen the fly's eye 
with this piece of apparatus in a way that I have never seen 
it before ; but by slightly varying the direction of the illumi- 
nation the surface of each lens might easily be made to 
appear, either concave or convex, and the same may be said 
of the glands in fractured specimens of coniferous wood. 
The Diatomacese supply admirable proofs of the efficiency 
and perfection of this illumination, and the markings may 
clearly be seen upon Pleurosigma formosum, angulatumy and 
fasciola ; but such specimens are best viewed when mounted 
on some dark absorbing material, and not on glass. The 
plan should also admit of the specimen being moved accu- 
rately into various positions. In looking at a valve of Helio- 
pelta, for instance, the raised portions show decided hexagonal 
walls, the depressed portions giving merely dots or points of 
illumination ; but one cannot find out where the two struc- 
tures merge into each other without tilting the specimen so 
as to get a view of the otherwise vertical plane. 
Perhaps the most striking objects are the scales from lepi- 
dopterous and other insects ; they can be seen by this method 
in a manner not to be approached by any other. I must 
confess to only a casual glance at a few specimens for their 
general beauty; but I noticed how remarkably well the long 
vertical and short transverse ribs could be seen on the scales 
of Morpho menelaus, and from what I have yet been able to 
see of the Podura scale, there is no reason for altering the 
description I have already given of it. 
We have been so long accustomed to the examination of 
objects that either are or have been made flat, that some 
persons hardly appear to understand the condition of many 
unprepared specimens. 
With this illumination, especially suited as it is for the 
highest powers, we often cannot expect to have more than a 
very small portion of the object in view at once, and in such 
cases the parts out of focus cannot be prevented from reflect- 
ing light, and giving a kind of indistinctness to the picture. In 
using this illumination I have generally found it best to put 
the light about eight inches from the microscope, and the 
reflector will then give an image of the flame upon the object. 
