28 CONSTRUCTION OF THE MICROSCOPE. 



which a rod 6 slides; this rod has at one end another but smaller joint 

 g, to which is attached a collar h, for receiving the lens 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 in- 

 creased 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 exami- 

 nation 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 microscope 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 supported on a firm tripod, made of bell-metal, the 

 feet of which, a a a, are made to close up for the purpose of packing it 

 in a box. The firm pillar b rises from the tripod, and carries the stage 

 e ', this is further strengthened by the two supports r r. 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 base d is moved up and 

 down within the triangular bar c, by turning the milled head t, forming 

 the coarse adjustment : this bar carries the lens-holder mnop. The 

 stage e consists 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 f t and has a spring clip h for holding, if necessary, 

 the objects under examination. By means of two screws placed dia- 

 gonally, one of which is seen at s, this elevated stage can be moved in 

 two directions, at right angles to one another; and thus different parts 

 of objects can be brought successively into the field of view. The arm 

 n p, for carrying the lenses, is attached to the triangular bar d by a 

 conical pin, on which it is made to turn horizontally, and the arm it- 

 self can be lengthened or shortened by means of the rack and pinion 

 m o ; hence the lens q can be applied to every part of an object without 

 moving the stage. 



The mirror I is fitted into the largest of the three legs, and consists 

 of a concave and plane glass reflector. To the under side of the stage 

 is fitted a Wollaston's condenser k ; and the lens is made to slide up 



