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The mechanical stage is in every sense mechanical. 

 The hands do not come in contact with the slide 

 except to place it on the stage. Two movements 

 are usually provided at right angles to one another, 

 either both with rack and pinion adjustment, or one 

 with rack and pinion while the other has a screw 

 motion. Examinations can be carried out with ease 

 and reliability under the highest powers. The main 

 value of the mechanical stage is that systematic 

 examinations over the entire surface of an object 

 can be carried on. 



Mirror and Mirror-bar. The proper illumi- 

 nation of an object is an important feature, and 

 although there are numerous accessories for properly 

 accomplishing this, which will be spoken of later on, 

 the mirrors alone are effective agents when properly 

 constructed and applied, particularly when no high 

 magnification is used. The plane mirror is usually 

 used on very low powers, and reflects light in about 

 the same intensity as its source. The concave mirror, 

 however, is intended to concentrate the light so that 

 all the rays which strike its surface are reflected 

 toward its optical axis and come together at some 

 point above it, and the rays from the surface being 

 contained within a comparatively small space, cause 

 an increased intensity, This point is called the focal 

 point, and is usually arranged to coincide with the 

 opening of the stage when parallel rays, such as 

 from the sky, are used. When the source of light 

 comes considerably nearer to the mirror, as for 



