40 Things not generally Known. 



HOW TO MAKE THE FISH-EYE MICROSCOPE. 



Very good microscopes may be made with the crystalline 

 lenses of fish, birds, and quadrupeds. As the lens of fishes is 

 spherical or spheroidal, it is absolutely necessary, previous to 

 its use, to determine its optical axis and the axis of vision 

 of the eye from which it is taken, and place the lens in such a 

 manner that its axis is a continuation of the axis of our own. 

 eye. In no other direction but this is the albumen of which 

 the lens consists symmetrically disposed in laminae of equal 

 density round a given line, which is the axis of the lens ; and 

 in no other direction does the gradation of density, by which 

 the spherical aberration is corrected, preserve a proper relation 

 to the axis of vision. 



When the lens of any small fi.sh, such as a minnow, a par, or trout, 

 has been taken out, along with the adhering vitreous humour, from the 

 eye-ball by cutting the sclerotic coat with a pair of scissors, it should be 

 placed upon a piece of fine silver-paper previously freed from its minute 

 adhering fibres. The absorbent nature of the paper will assist in re- 

 moving all the vitreous humour from the lens ; and when this is care- 

 fully done, by rolling it about with another piece of silver-papei", there 

 will still remain, round or near the equator of the lens, a black ridge, 

 consisting of the processes by which it was suspended in the eye-ball. 

 The black circle points out to us the true axis of the lens, which is per- 

 pendicular to a plane passing through it. When the small crystalline 

 has been freed from all the adhering vitreous humour, the capsule which 

 contains it will have a surface as fine as a pellicle of fluid. It is then to 

 be dropped from the paper into a cavity formed by a brass rim, and its 

 position changed till the black circle is parallel to the circular rim, in 

 which case only the axis of the lens will be a continuation of the axis of 

 the observer's eye. Edin. Jour. Science, vol. ii. 



LEUWENHOECK'S MICROSCOPES. 



Leuwenhoeck, the father of microscopical discovery, com- 

 municated to the Royal Society, in 1673, a description of the 

 structure of a bee and a louse, seen by aid of his improved mi- 

 croscopes ; and from this period until his decease in 1723, he 

 regularly transmitted to the society his microscopical observa- 

 tions and discoveries, so that 375 of his papers and letters are 

 preserved in the society's archives, extending over fifty years. 

 He further bequeathed to the Royal Society a cabinet of twenty- 

 six microscopes, which he had ground himself and set in silver, 

 mostly extracted by him from minerals; these microscopes were 

 exhibited to Peter the Great when he was at Delft in 1698. In 

 acknowledging the bequest, the council of the Royal Society, 

 in 1724, presented Leuwenhoeck's daughter with a handsome 

 silver bowl, bearing the arms of the society. Weld's History 

 of the Royal Society, vol. i. 



DIAMOND LENSES FOR MICROSCOPES. 



In recommending the employment of Diamond and other 



