THE "STEPHMNSON* PRISMS. 



35 



prisms A A, Fig. 20, which, passing upwards, are reflected 

 towards the eye-pieces by the triangular prism B, Fig. 21. 

 The instrument is erecting that is to say, objects are pre- 

 sented to the eye in a normal manner, and not inverted 

 as in the ordinary form of instrument, which adapts it 

 specially for use in dissecting. The bodies of the micro- 

 scope are made to rotate, carrying the prisms with them, 

 so that two observers may work with the instrument, 



FIG. 20. 



FIG. 21. 



observe the same object, and compare notes without alter- 

 ing the conditions under which the object is being 

 examined. 



Amongst the foregoing medium and best stands, the 

 reader must be fastidious indeed if he is not able to find 

 one to suit his choice. Price might be a deterrent, and 

 therefore some illustrations are given of several microscopes 

 which, though cheap, are good working instruments. 



Fig. 22 is the Economic monocular microscope of Messrs. 

 R. and J. Beck, which with coarse and fine adjust- 

 ment, I -inch and J-inch objectives, two eye-pieces, con- 

 cave mirror, side condensing lens, diaphragm, forceps, 

 pliers, and glass slip with ledge, in mahogany case, costs 

 61. I2s. 6d. A small cheap stand such as this is nearly 

 always required by the practical microscopist, even if he 

 possesses a first-rate instrument; for travelling, Society 



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