4(5 SELECTION AND USE 



Binocular Dissecting Microscope. The binocular 

 principle, when applied to the dissecting microscope, is of the 

 greatest value, as it enables us to estimate accurately the posi- 

 tions, vertically, of the several parts, and we can thus direct 

 needles, knives, scissors, etc., to the exact point that we wish to 

 operate on with an accuracy that is impossible with the monocu- 

 lar dissecting microscope. Nachet and Beck manufacture very 

 excellent binocular dissecting microscopes, and the only thing 

 to be regretted is that the price is necessarily somewhat high. 



PRINCIPAL FORMS OF THE COMPOUND 

 MICROSCOPE. 



The variety of models, styles, or patterns which have been 

 devised for the stands and for the general arrangement of com- 

 pound microscopes, is almost infinite, and as they are con- 

 tinually changing, it would be a hopeless task to attempt to 

 give a description of all, or even of any large number of them. 

 Fortunately, from motives of self-interest, the manufacturers of 

 these instruments promptly publish full descriptions and en- 

 gravings of new styles as soon as they bring them out, and 

 thei'efore the best plan for those who desire to make a judicious 

 selection, is to procure the catalogues of as many manufacturers 

 as possible, and carefully compare the several advantages of the 

 different forms. The addresses of all the prominent manufac- 

 turers are published from year to year in the " Microscopist's 

 Annual," a cheap little volume devoted to statistical informa- 

 tion of this kind. 



Cheap Foreign Stands. -A few years ago, the only 

 stands attainable by those who could not afford an expensive 

 article, were the cheap French and German microscopes. 

 These were imported in large numbers by dealers in optical 

 goods, and were distributed to different parts of the country 

 through the agency of watchmakers, jewellers, booksellers, and 

 those who dealt in spectacles and opera glasses, and conse- 

 quently were called "opticians." Fortunately the production 

 of really good and cheap American microscopes has almost 

 driven this class of instruments out of market, but as they are 

 still to be found on sale, a few words in regard to them may bo 



