10 GORHAM, ON THE 



of the wonderful arrangement whereby upwards of twelve 

 thousand planes, each a perfect hexagon, are packed in a bit 

 of membrane scarcely so large as half the little finger nail. 

 " I have often," says the celebrated Leeuwenhoek, " made re- 

 peated dissections of the eyes of various kinds of insects, 

 merely on account of the pleasure the contemplating them 

 afforded me."* But few, however, seem inclined to investi- 

 gate these subjects for themselves, trusting rather to that 

 second-hand kind of knowledge derivable from books. This 

 distaste for exploring the works of nature may possibly, in 

 some instances, commence with the limited resources of the 

 pocket ; the very preparation of a microscopic object in- 

 volving the necessity for a costly instrument wherewith to 

 investigate it. If, however, I shall succeed in pointing out 

 certain beauties peculiar to the compound cornea in the eye 

 of the insect, which may be discovered with the naked eye, 

 and without a microscope, this membrane will have become 

 invested with a new interest, and thus others may be stimu- 

 lated to a like inquiry. But to return. Having inserted a 

 slide containing a circular section of the eye of the dragon-fly 

 in the box prepared for the purpose, I proceeded to examine 

 it. Recalling to mind, however, that each of the hexagonal 

 facets is barely the six-hundredth of an inch across, and that 

 many hundreds of such facets are contained in the smallest 

 section, it was much to anticipate that such a structure should 

 be resolved by a process so simple ; and when on viewing the 

 membrane, by looking at it through the small aperture, while 

 a lighted candle was held nearly close to the larger one, it 

 presented a semi-opaque and altogether homogeneous appear- 

 ance, I had almost concluded that my efforts were frustrated. 

 To overcome the difficulty was reserved, however, for a future 

 trial. Now if, instead of a candle, a small wax taper be used, 

 and if this be held at the distance of from five to nine feet, 

 rather than close to the large aperture, a beautiful sight pre- 

 sents itself. Instead of the flame of one taper, there are 

 exhibited the miniature images of the flames of many tapers ; 

 and these are not only very definite in their outline so as to 

 be immediately identified, but they are arranged at regular 

 intervals. But, what is still more curious, each image, except 

 the central one, is seen to be composed of the colours of the 

 prismatic spectrum, — violet, indigo, blue, green, yellow, 

 orange, and red ; of which the extreme tints are so disposed 

 that the blue portion in each image is always nearest to the 

 central or colourless flame, and the red tlie most remote from 

 it. Hence the blue and the red tints alternate in concentric 

 * Leeuwenhoek, vol. ii. p. 341. 



