DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 105 



small milled head. These milled heads T place on the 

 same side as the large milled head, x, which works in the 

 rack of the triangular bar, so that all the motions are 

 obtained by one hand, whilst the other is left quite at 

 liberty. 



Fig. 18. 



In the annexed figure, 18, a plan of this stage is given. 

 It fits into the block of my instrument by means of two 

 pins, just in the same manner as the other stages, &c. are 

 made to do. 



e, and/, are the two milled heads for effecting the 

 lateral motion. The former of these is connected with 

 the screw, and will move the stage to the right or left, 

 the latter to the pinion, and will move the stage to and 

 fro. By turning both the milled heads, therefore, at the 

 same time, a diagonal motion (by the composition of 

 forces) will be obtained, by which the object for inspec- 

 tion can be brought and retained in the axis of the in- 

 strument, y, y, are two studs for the purpose of carrying 

 the arm d, at the further extremity of which a pair of 

 forceps (fig. 15) may be inserted for holding an insect, or 

 any other object which may be required. The studs 

 will support also a plate of glass when the instrument is 



