514 



SUMMARY OF ODIU^ENT RESEARCHES RELATING TO 



Fig. 100. 



The foundation of the stand is a solid cast-iron base A, having at 

 its top a hinge-joint B, wliich allows the instrnnicnt to be inclined at 

 any angle, and is sufficiently firm to permit of its being placed hori- 

 zontal for nse with Wollaston's camera lucida. The body D has a 

 draw-tube C, with coarse and fine adjustments at N and F. The stage 

 G has two springs H H, the pins attached to which may he inserted 

 in any of the four holes on the stage, and by tlieir pressure ( whicii 

 can be varied by pushing thera more or less down) will hold the 

 object under them or allow it to be moved about with the greatest 

 accuracy. '1 he mirror J, besides swinging in the rotating semicircle K, 

 is attached to a bar L, witli a joint at each end allowing a lateral 

 movement, so as to throw oblique light on the object. An iris dia- 

 l^hragm M, in which the size of the aperture is varied by revolving 



it in its fitting, screws into 

 the under surface of the 

 stage, and can be removed 

 when other substage ap- 

 paratus is required. 



Class Microscopes. — M. 

 Nachet's instrument (fig. 

 100) is an attempt to cope 

 with the mischievousncss of 

 youth, whose eccentricities 

 are liable to invade even the 

 domains of Microscopy. 



All the adjustable parts 

 are locked by a removable 

 " key," the large milled head 

 of which is shown near the 

 objective. Tluis the eye-piece 

 is fixed so that it cannot bo 

 moved ; the body-tube can 

 only be raised or lowered by 

 the ajiplication of the key to 

 a pin at the top of the pillar 

 (concealed by the ornamental 

 cap, which is unscrewed) ; 

 the objective is rendered 

 immovable by the same 

 means, the key acting on a 

 screw which passes through 

 the projecting piece, whilst 

 the mirror has no milled 

 heads to the axis, and can 

 only be turned by the key. 



The slide is fastened down by two bars, one of which is shown 



slightly raised in the figure. 



The only part left free is the fine adjustment, which is effected 



by turning the handle seen at the base of the pillar, which slightly 



raises or lowers the body-tube. An index shows the extent of move- 



