BRO WNINGS PLA TVS CO PIC LENSES. 5 



where a high power is not required ; they are cheap, but 

 the lower powers only are generally useful. The Stanhope 

 and Coddington lenses are also used by some collectors, 

 though there is little doubt that they are going out of date 

 on account of their not being so useful as newer forms of 

 the simple microscope. 



The Stanhope magnifier is a double convex lens having 

 two unequal curvatures. In observing, the deepest curve 

 is placed towards the eye, the object 

 adhering to the least convex side being 

 just in focus. The Coddington lens is 

 generally a sphere of glass, round the 

 periphery of which a deep groove has 

 been cut and filled up again with black 

 cement. This lens focusses at a short 

 distance from the object, and is much 

 superior to the Stanhope form. Inferior p 



Coddingtons are now made from re- 

 jected double convex lenses which do not act as well as 

 the form described. 



Without doubt the best magnifiers for field use and 

 such work generally are the platyscopic lenses of Mr. 

 John Browning, which he makes of three degrees of 

 power, amplifying 15, 20, and 30 diameters respectively. 

 They are really achromatic triplets, are set in ebonite 

 cells, and mounted in tortoise-shell frames. These 

 lenses focus at about three times the distance from an 

 object as a Coddington of the same power, and so allow 

 of the easy examination of opaque objects. They are 

 shown engraved full size in Fig. 2. Steinheil has produced 

 similar lenses, which he terms " aplanatische loupen " ; they 

 are of similar construction to the above, and are made to 

 magnify 5j, 8, 12, 1 6, and 24 diameters. 



One of these lenses, or, preferably, two of them, carried 



