MICROSCOPIC DRAWING AND ENGRAVING. 



of Mr. Froment. 12. Rectangular scales. 13. Micro-metric 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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