80 THE MICROSCOPE. 



cealed by the stage-fittings) is attached to the other end of 

 the axis of the pinion (as in fig. 39), so as to be "worked 

 with the left hand. The "fine" adjustment is effected by 

 the milled-head on the transverse arm, just behind the base 

 of the " body." This acts upon the " nose " ur tube pro- 

 jecting below the arm, wherein the objectives are screwed. 

 The other milled-head seen at the summit of the stem 

 serves to secure the transverse arm to this, and may be 

 tightened or slackened at pleasure, so as to regulate the 

 traversing movement of the arm. This movement is only 

 allowed to take place in one direction ; namely, towards 

 the right side, being checked in the opposite by a " stop," 

 which secures the coincidence of the axis of the body with 

 the centre of the stage, and with the axis of the illu- 

 minating apparatus beneath it. It is in the movements 

 of the stage that the greatest contrivance is shown. These 

 are three ; namely, a traversing movement from side to 

 side, a traversing movement from before backwards, and 

 a rotatory movement. The traversing movements, which 

 allow the platform carrying the object to be shifted about 

 an inch in each direction, are effected by the two milled- 

 heads situated at the right of the stage ; and these are 

 placed side by side, in such a position that one may be 

 conveniently acted on by the fore-finger, and the other by 

 the middle-finger, the thumb being readily passed from one 

 to the other. The traversing portion of the stage carries 

 the platform whereon the object is laid, which has a ledge 

 at the back for it to rest against ; and this platform has 

 a sliding movement of its own from before backwards, by 

 which the object is first brought near to the axis of the 

 microscope, its perfect adjustment being then obtained 

 by traversing movements. To this platform, and to the 

 traversing slides which carry it, a rotatory movement is 

 imparted by a milled-head placed underneath the stage 

 on the left-hand side ; for this milled-head turns a pinion 

 which works against the circular rack (seen in the figure), 

 whereby the whole apparatus above is carried round about 

 two-thirds of a revolution, without in the least disturbing 

 the place of the object, or removing it from the field of 

 the microscope. This rotatory movement is useful for twc 

 purposes — first, in the examination of very delicate objects 



