G. C. KAROP ON POCKET MAGNIFIERS. 



503 



overlooked until it was re-invented by Bruecke years afterwards, 

 and it is now used for dissecting and other purposes. 



Plossl, according to Harting, was the first to construct 

 magnifiers, in the limited sense, with achromatised lenses, 

 though he does not give their composition. At the present 

 day the triple cemented combinations known as " Steinheil " 

 lenses, a thick biconvex centre and a meniscus at each end, 

 have practically supplanted all the earlier forms ; when well 

 made, these are undoubtedly of great excellence, and for certain 

 purposes unsurpassed. 



The celebrated Dutch naturalist Leeuwenhoek appears to have 

 been the first to construct a reflector microscope, a concave 

 sjDOculum with a lens in the centre (Letter to the Royal Society 

 of London, January 1689). But it was Lieberkiihn who brought 

 this form of instrument into prominence, about 1738. In its 

 primitive pattern it was applicable to any number of small 

 opaque objects, being furnished with a stage forceps adjustable 

 to its focus. The later, and, from pictures at least, better known 

 instruments, however, had the considerable drawback of being 

 restricted to a single object — one microscope, one specimen — 

 beautiful as these may have been. 



It is rather singular that some similar type of reflecting magni- 

 fier, which possesses obvious advantages to the field naturalist. 



Nelson. 



Swift. 



should not have survived, but until recently I cannot call to mind 

 anything of the kind. Some two or three years ago, Mr. Nelson 

 turned his attention to this hiatus in our modern equipment, and 

 devised a very ingenious reflecting magnifier of somewhat peculiar 

 construction. It consists of a thick inequi-convex let into a 

 plano-convex, the curved surface of which is silvered, and on 

 its lower plane surface a plano-convex, of about the same size 

 as the biconvex, is cemented. When held towards the light 

 the silvered surface reflects and concentrates the rays upon the 

 object held in the focus of the combination. Mr. Nelson's 



