MAGNIFYING POWER OF SHORT SPACES. 9 



With this simple apparatus I could examine very small 

 transparent objects at pleasure, either by the light of the sun 

 or of a taper. Whilst, however, it has been thought better to 

 notice the dimensions of the apertures, &c., for the conveni- 

 ence of others who might wish to repeat the experiments, it 

 must not, by any means, be supposed that they are the best 

 adapted to insure success, or that better could not be devised. 



Having been engaged in the preparation of a series of dis- 

 sections of the comjwund cornea of the eye in insects, I naturally 

 subjected one of these beautiful objects to the first experiment 

 in my lens-less microscope. Here, however, for the informa- 

 tion of those who may not be conversant with these objects, or 

 the peculiarities of their structure, it may be remarked that 

 the roundish, prominent, transparent elevations observed, 

 generally one on each side of an insect's head, constitute the 

 membrane in question. This membrane forms at once the 

 defence and the covering to the delicate parts in the interior 

 of the eye, as well as the transparent medium by which the 

 light is admitted into this tiny organ. It is analogous, more- 

 over, to the transparent cornea of the eye in the higher classes 

 of animals in being transparent, composed of several firmly- 

 adhering layers, and forming the outermost of all the coverings 

 of the eye. But it is altogether dissimilar in this respect, 

 that it is found to consist of an immense number of facets or 

 little pieces lying, side by side, like fine mosaic ; and which 

 from being of a regular hexagonal shape, and arranged in 

 perfect order, present when examined under the microscope 

 an appearance like a honeycomb. Hence it has received the 

 name of compound cornea. 



The eye of the large insect, called the dragon-fly, is recom- 

 mended for a first trial in dissection, because it is not only 

 very large but exceedingly beautiful. The compound cornea 

 is at once separated from the rest of the eye with a pair of 

 finely-pointed scissors, and the dark thick pigment which fills 

 the inside is then washed away by soaking in a tumbler of 

 cold water for an hour or two, and then using a camel's-hair 

 pencil. To procure it in a perfectly clean and transparent 

 state, however, it is better to wash and rewash it after macera- 

 tion for two days in frequently-changed cold water. Then, 

 while still moist, let small circular pieces be excised with a 

 small punch, and pressed immediately between two slips of 

 glass. In a few days they will have become dry and flat, and 

 may then be mounted in what is called the dry way, as if for 

 the microscope. 



I wish it was in my power to convey to my readers an idea 

 of the great beauty of one of these specimens ; to say nothing 



