36 CONSTRUCTION OF THE MICROSCOPE. 



slides another slaort tube c, carrying at its top a joint /; 

 to this joint is fixed a square tube a, through which a rod 

 h sHdes; this rod has at one end another but smaller 

 joint g, to which is attached a collar h, for receiving the 

 l«ns i. By means of the joint at/, the square rod can be 

 moved up or down, so as to bring the lens close to the 

 object; and by the rod sliding through the square tube a, 

 the distance between the stand and the lens may be either 

 increased or diminished : the joint g, at the end of the 

 rod, is for the purpose of allowing the lens to be brought 

 either horizontally or at an angle to the subject to be 

 investigated. By means of the sliding arm the distance 

 between the table and the jointed arm can be increased 

 or diminished. This microscope is provided with lenses 

 of one-inch and half-inch focal length, and is thereby 

 most useful for the examination and dissection of objects. 

 It is readily unscrewed and taken to pieces, and may be 

 packed in a small case for the pocket. 



Another highly-useful and more complete simple micro- 

 scope was contrived by Mr. W. Valentine, and made for 

 him by Mr. Ross in 1831. It is thus described by the 

 latter gentleman, and is represented in fig. 24. It is sup- 

 ported on a firm tripod, made of bell-metal, the feet of 

 which, aaa^ are made to close up for the purpose of pack- 

 ing it in a box. The firm pillar b rises from the tripod, 

 and carries the stage e ; this is further streng-thened by the 

 two supports rr. From the pillar a triangular bar d, and 

 a triangular tube c, is moved up and down by a screw, 

 having fifty threads in the inch, and turned by a large 

 milled head v, which is situated at the base of the pillar : 

 this is the fine adjustment. The small triangular bar d 

 i« moved up and down within the triangular tube c, by 

 turnmg the milled head t, forming the coarse adjustment : 

 this bar carries the lens-holder mnop. The stage e con- 

 sists of three plates ; the lowest one is firmly attached to 

 the pillar, and upon this the other two work. The upper 

 one carries a small elevated stage g, on which the objects 

 are placed ; this stage is mounted on a tube /, and has a 

 spring clip h, for holding, if necessary, the objects under 

 examination. By means of two screws placed diagonally, 

 one of which is seen at .s- this elevated stajre can be moved 



