64: 



THE MICROSCOPE AND ITS REVELATIONS. 



jecting piece on either sido, into which may be screwed a pin that 

 carries a sliding-spring; this arrangement is suited for securing a 

 Zoophyte-trough or other piece of apparatus not suitable to being 

 received by the object carrier, which can be easily slipped away from 

 beneath the ivory knobs, thus leaving the stage free. To the under side 

 of the stage is firmly pivoted a broad bar, into which is screwed a short 

 sprung tube, that becomes exactly concentric with the optic axis of the 

 instrument, when the bar (which is shown turned away in the figure) is 

 pushed beneath the stage until checked by a firm stop; and as this bar is 

 composed of two pieces, held together "by a pair of screws working 

 through slots, the centering of the tube may be precisely readjusted if it 

 should at any time become faulty. Into this tube may be inserted 

 another that carries either (1) a Diaphragm, sliding with caps of differ- 



Fir,. 40. 



Nachet's Student's Microscope. 



Browning's Rotating Microscope. 



ent apertures; (2) a Polarizing prism; (3) a Ground-glass for diffusing 

 the light, which may be either plane, or a plano-convex lens ground on 

 its flat side which is directed upwards; (4) an Achromatic Condenser; 

 and (5) a Glass Cone, having its apex pointing downwards, and a large 

 black spot in the centre of the convex base directed towards the object, 

 which gives an excellent * black-ground ' illumination. Lastly, the 

 Mirror is attached to a stem which is so jointed as to enable it to reflect 

 rays of very great obliquity. To those who wish a compact instrument 

 of great completeness and capability, which may be worked advantage- 

 ously even with high powers, the, Author can strongly recommend this 



