THE SIMPLE MICROSCOPE. 



49 



and, consequently, the aberration is trifling. This lens gives 

 a large field of view, equally good in all directions, and it 

 B A little matters in what position it is held, hence 



it is peculiarly applicable as a hand magnifier. 

 The lens is generally set in silver or German 

 silver, as represented by fig. 26, and the handle 

 is so contrived, that it occupies 

 but little room in the waistcoat 

 pocket. It may be as well 

 here to mention that many of 

 the lenses sold as Coddington 

 lenses are not constructed after 

 this manner, but are made up 

 of two convex lenses, not por- 

 tions of spheres, hence they are 

 destitute of many of the advan- '^' 



tages of the true Coddington lens. Another 

 lens, somewhat of the same description as the 

 Fig. 23. last, is much boasted of by its manufacturers, 

 and is puffed off at every toy-shop as the Stanhope lens ; it 

 consists of nothing more than a double convex lens of great 

 thickness, on one side of which the convex surface is greater 

 than on the other; and when the most convex is turned 

 towards the eye, an object placed upon the other convex sur- 

 face is in the proper focus of the lens ; it is, in consequence, 

 generally used more as a toy. than as a philosophical instru- 

 ment, for viewing the scales of butterflies' wings and other flat 

 objects which can readily be attached to it, or for showing the 

 eels in paste, and the wonders in a drop of water. If, how- 

 ever, the flattest side be turned towards the eye, this form of 

 lens may also be used as a magnifier, its focus being then from 

 1^ to ^ of an inch. 



When any of these lenses have to be held for a long time 

 in the hand, much inconvenience wiU be felt, hence various 

 stands or supports have been contrived by which the magnify- 

 ing power may be kept in a fixed position over the desired 

 object. The engraver, the watchmaker, the jeweller, and the 

 artist, all require some form of lens, and each has an appa- 

 4 



