THE STUDENT'S MICROSCOPE. 65 



which gives additional stability ; they support, at their 

 upper part, the trunnions to which the tube and the 

 stage are attached. From out the tube a triangular 

 bar is raised by a rack and pinion connected with the 

 milled head. To the upper part of the triangular bar 

 a broad arm is fixed, bearing the compound body; this 

 arm is hollow, and contains the mechanism for the fine 

 adjustment, which is effected by turning the small milled 

 head. The arm is connected with the triangular bar by 

 a strong conical pin, on which it turns, so that the com- 

 pound body may be moved aside from the stage when 

 necessary ; by a mechanical arrangement it stops when 

 central. The stage is of an entirely new construction, 

 having vertical, horizontal, and circular movements, and 

 graduated for the purpose of registering objects so as to 

 be found at pleasure ; and in order to do this effectually 

 a clamping piece is provided against which the object slide 

 rests, and the circular motion of the stage is stopped. It 

 is an exceedingly effectual method of finding any favourite 

 object. The stage is remarkably strong, and at the same 

 time so thin, that the utmost obliquity of illumination is 

 attainable, the under portion being entirely turned out : it 

 has a dove-tailed sliding bar moveable by rack and pinion, 

 on turning the milled head into this bar slides the under 

 stage, having vertical and horizontal motions for centering, 

 and also a circular motion ; into the stage are affixed 

 the various appliances for underneath illumination. The 

 achromatic condenser, if of 100 of aperture, with nine 

 apertures and five central stops, the apertures and stops 

 having independent movements, the manipulator can 

 regulate at will ; this is considered to be a great improve- 

 ment. There is an appliance provided for the dark- wells, 

 which is put into the dove- tailed sliding bar instead 

 of the underneath stage. The mirror is attached to a 

 quadrant of brass and two arms, in order to obtain greater 

 obliquity of illumination ; the whole fits into a short piece 

 of tube made to slide either up or down the long tube 

 attached to the bottom of the stage by which the mirror 

 is connected with the other part of the stand; the re- 

 flectors themselves are both plane and concave, as in other 

 instruments. The achromatic prism for oblique light ia 



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