ON CONSTRUCTING STANDS OF MICROSCOPES. 157 



The stage must also possess a capability of turning 

 round on a pivot, so that by tilting the microscope we 

 may be enabled to view the side or elevation of a body 

 as well as its plan ; for example, the curve of a small 

 lens, when laid flat on its face, the edge of a razor, the 

 point of a needle, &c. without using any particular ap- 

 paratus to preserve such bodies in the position in which 

 we wish to see them. The use of such a mode of ob- 

 serving, in cases of dissection, must be manifest; for in 

 this way the side of an insect, &c. may be viewed and 

 worked upon without disturbing the parts laid open, in 

 the horizontal position, and thereby occasioning much 

 extra trouble and confusion. By turning the subject 

 round on the stage, every elevation or side view of it may, 

 of course, be successively obtained. 



There is yet another advantage to be gained by a rota- 

 tory motion in the stage; for if we employ a diagonal 

 objective, and tilt both the stage and the bar into a hori- 

 zontal position, so that the body of the microscope shall 

 be under the stage, we can examine crystallizations of 

 salts without being annoyed by the steam which arises 

 from them during consolidation, and which is almost 

 certain to condense on the object glass when used in any 

 other position. In the present case this is impossible; 

 for nothing but the under surface of the glass on which 

 the salt is placed, is presented towards the object glass. 

 All sorts of fluids, and the bodies contained in them, may 

 in the same way be managed without being troublesome, 



