266 THE SIMPLE MICROSCOPE. 



0. The Mechanical Arrangement. 



Of the mountings of lenses and systems of lenses, as well as of 

 the stands, we shall treat very briefly, since every well-known 

 optical establishment is able to satisfy on these points all demands 

 which can reasonably be made. The observer must choose for 

 himself among the various forms and arrangements supplied, that 

 which best meets his requirements. If any very special end is in 

 view, he will probably devise a suitable apparatus. 



The lens-carriers described in micrographic works all agree in 

 this point that they are furnished with a movable arm, often 

 jointed, which is attached to a box or to a vertical pillar so that 

 its free end carrying the lens can be adjusted as required. 



The stand of a simple Microscope admits of some variety of 

 design. The principal requirements which the optician should bear 

 in mind are the following : (1) A firm not too small object- 

 stage, to which a spring-clip or other suitable contrivance for 

 holding the object-slides can be applied ; (2) a convenient support 

 for the hand whilst making dissections upon the stage ; (3) an 

 arrangement of the rapid focusing adjustment by which the lens 

 is moved towards the object the latter remaining stationary ; (4)- 

 an illuminating apparatus providing cones of light that wholly 

 occupy the aperture of the system of lenses or the pupil of the eye. 



[Here, again, it has been thought preferable to omit the authors' 

 descriptions of the simple Microscopes 1 for the reasons assigned on 

 p. 122.] 



1 The following simple Microscopes are described in the German work : 



OPTICIANS. MICROSCOPES. 



Sachet & Son (Paris) . . Lens-carrier, recommended by Mohl,"Mikrographie,"" 



p. 35 (Fig. 149). 



C. Zeiss (Jena) . . . . Small dissecting (Fig. 150). 

 .. .. Large (Fig. 151). 

 Beneche (Berlin) . . Two, similar to Zeiss's, the fine adjustment like- 



Nobert's. 



Schieck (Berlin) . . One, similar. 



S. Ploessl & Co. (Vienna) One, focusing by the stage. 

 Nachet & Son (Paris) . . Dissecting (Fig. 152). 

 ,, ,, . . Binocular dissecting. 



Quekett . . . . Pocket and dissecting (Fig. 153). 



Pritchard . . Dissecting (Fig. 154). 



