176 



MICROSCOPIC OBJECTS. 



Description of Engraving. — ^The eye-piece is seen at tt, 

 the body at b, and the object-glasses are screwed into the 

 bottom of the tube or body at d. The arm c is attached 

 to the top of the triangular gun-metal bar e, and has a 

 motion round the latter. The large milled head, /, has 

 a pinion which works into the teeth of the rack e, and 

 sei*ves to raise and lower the body, and thus adjust the 

 distemce to the focus of the lenses, g is the stage upon 

 which the objects for examination are to be placed. This 

 stage has four holes at its corners, which serve to hold a 

 pair of forceps, or to pass a string through when viewing 

 the circulation of the blood in a frog's foot, the frog 

 being previously fastened to a piece of wood or lead in a 

 cloth bag. In the centre of the stage is a black annulus, 

 which can be removed when viewing opaque objects with 

 a silver cup. h is the stem of the microscope, i the 

 triangular pedestal, and 7 the mirror. 



Additions to this Instrument relate chiefly to the optical 

 part. They , consist, first, of additional sets of object- 



glasses and eye-pieces for giving a greater range of 

 magnifying powers, as shown in the table given in 

 page 179. The above engraving shows two eye-pieces, the 



