76 PEACTICAL TEEATISE ON THE MICROSCOPE. 



wide, and three-and-a-half inches apart, this Tjeing equivalent 

 to a triangular bar of the same size. The fine adjustment is 

 made by a screw with a cone, against which the cradle, or 

 portion of brass attached to the body, is firmly pressed by 

 means of a spring ; one of the milled heads of the fine adjust- 

 ment is seen at B. By this method of mounting the com- 

 pound body, all tendency to run down by its own weight is 

 prevented, in consequence of its motion being that of a 

 sliding combined with a rolling one. The lower part of the 

 arm carrying the compound body at I is provided with a 

 conical pin fitting into the piece of metal supporting the 

 stage; by this a circular motion is obtained, and the body 

 can be turned away from the stage, so that an object placed 

 upon it can be properly adjusted before the body is brought 

 over it. The stage is of the form first constructed by Mr. 

 TurreU, and described by him in the forty-ninth volume of 

 the Transactions of the Society of Arts. It has a motion each 

 way of three-quarters of an inch in extent, that from side to 

 side being effected by a screw turned by the milled head C, 

 whilst the up and down motion is performed by a rack and 

 pinion in connection with the milled head D. The stage- 

 plate has a circular motion, and on it is a spring clip H for 

 seciuiag the objects when the instrument is inclined. A 

 small arm E is seen underneath the stage; this carries the 

 dark weUs, to be used when minute opaque objects are iUu- 

 minated by the Lieberkuhn. The mirror is mounted rather 

 differently from those supplied with other microscopes ; instead 

 of a semicircle of brass with two pins, on which the frame 

 containing the reflectors may turn, there is a quadrant of 

 brass, having at one end a strong pin on which the frame is 

 turned up or down, and at the other end a still stronger one, 

 on which the quadrant and the frame together are capable of 

 being revolved; this last 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 reflectors themselves 

 are both plane and concave, as in other instruments. With 

 this microscope are supplied an achromatic condenser, a 



