MICROSCOPIC DRAWING AND ENGRAVING. 
of Mr. Froment.— 12. Rectangular scales.— 13. Micrometric threads. 
—14. Necessity for microscopic tests.— 15. Test-objects.— 16. Tele¬ 
scopic tests ; double stars.— 17. Nebulae and stellar-clusters. —18. 
Effects of different telescopes upon them : telescopes of Herschel and 
Lord Rosse.— 19 . Remarkable nebulae described by Herschel.— 20 . 
Differently seen by Lord Rosse.— 21 . Microscopic tests.— 22 . Im¬ 
proved powers of microscope.— 23. The Lepisma-Saccharina.— 24* 
The Podura, or Spring-tail. 
1. No person can witness without the highest degree of admi¬ 
ration the spectacle presented by certain parts of the structure of 
the more minute members of the animal kingdom, when viewed 
with a powerful microscope. The absolute geometrical precision 
and extreme beauty of design shown in such objects, are truly 
remarkable. We will not say, that such perfection of workman¬ 
ship discovered in these minute objects, which must have for ever 
escaped the human eye without the intervention of scientific aid, 
ought to excite surprise, because no result, however perfect, of 
infinite power combined with infinite skill should raise that senti¬ 
ment. Nevertheless, it must be admitted, as a matter of fact, 
that the contemplation of such objects is generally attended with 
a sense of wonder, approaching to awe, a striking proof how few 
they are that have sufficiently familiarised their minds with the 
ideas of omnipotence and omniscience. 
2. Innumerable examples of the perfect precision of structure, 
adaptation and design, combined with a minuteness, which not 
only far surpasses the limits of the senses, but severely taxes the 
imagination, are presented in the organisation of natural objects. 
The membrane, which in the eyes of certain species of insects cor¬ 
responds to the cornea of the human eye, presents an example of 
this, A. very exact notion of this membrane, as it exists in the 
eye of the common house-fly, may be obtained by stretching a piece 
of bobbin-net over the surface of a billiard-ball: the ball with its 
reticulated hexagonal coating will then be a very precise model of 
part of the eye of the insect, upon a prodigiously magnified 
scale. 
We have given in fig. 1 an engraving of this membrane, taken 
from a microscopic drawing, magnified 100 times in its linear, 
and therefore 10000 times in its superficial dimensions. 
3. Each hexagon, as shown in the figure, is the cornea of a 
separate eye, having behind it the proper optical apparatus to pro¬ 
duce the sense of vision. But it is more particularly to the mi¬ 
nuteness of these beautifully precise hexagonal eyes, that I desire 
at present to direct attention. That minuteness will be most strik¬ 
ingly manifested by stating the number of these eyes with which 
different classes of insects are provided. According to the obser¬ 
vations of various eminent naturalists, such as Swammerdam, 
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