102 THE MICROSCOPE. 



slides, and a spring-notch shows the axial position. 

 The sliding fitting allows the mirror to be placed some 

 distance out of the axis radially, and then the rotation 

 of the circular moving base plate gives a considerable 

 range of obliquity of light in azimuth ; the light from 

 the mirror remaining constantly directed upon the 

 object, this facility obtains with all inclinations of the 

 limb and stage, because the object itself forms the centre 

 both of the azimuthal rotation and of the inclination 

 in altitude. The limb is mounted in a " cradle " joint, 

 at the top of the pillar, permitting inclination from the 

 perpendicular. 



The angle of inclination is registered upon a gradu- 

 ated ring against the clamping screw. The optical 

 body is mounted, not as usual on the front of the 

 " Jackson " limb, but on the side of it; thus converting 

 the side of the limb into the front. 



The coarse-adjustment is by the ordinary rack and 

 pinion ; the fine- adjustment lifts the optical body in a 

 separate slide-fitting by means of a wedge-shaped block 

 acted upon by the conical end of a fine micrometer- 

 screw. The focal distance can be measured by the 

 scale engraved on the slide-fitting. 



The stage is of the newest construction, and beneath 

 which is the sub-stage arm, carrying the usual screw- 

 centring and rack-adjusting sub-stage, so attached to a 

 sector in the rear of the stage in which it traverses 

 concentric with the object. The sub-stage bar also 

 carries the usual centring fitting for condenser, etc., 

 and swings forwards or backwards concentric with 

 the object on the main stage, and the obliquity of the 

 swing can be registered on a graduated ring imme- 

 diately behind the stage. The construction is similar 

 to that of the Ross-Zentmayer. An extra swinging 

 bar is attached behind, into which the mirror can be 

 slid for use in combination with the condenser, etc. It 

 should be noticed that there is a third divided circle 

 on the sub- stage sector giving the inclination of the 

 sub-stage to the axis of the body. A strong clamp ou 

 the other side of the cradle joint holds the body firmly 

 at any inclination, and a graduation on the slide of 



