770 



COMPOUND MICEOSCOPE. 



r 



and in 949 it is mounted. The woodcuts are exactly wne-half the real 

 size, and give a good idea of the instrument, a detailed description of 

 which is not required. In fig. 950 a representation is given of one of 

 Smith and Beck's microscopes for students. A is the brass stand, sup- 

 ported firmly on three feet, and having two upright flat cheeks, to the 

 top of which the stage-plate, d, is fixed. Into the stage-plate is 



screwed an upright round tube, 

 to which is attached an open 

 tube, g, in which the body of 

 the instrument, fh, slides. By 

 moving the body up and down 

 in this tube, the coarse adjust- 

 ment is effected, and when the 

 instrument is brought near to 

 the object on the stage-plate, 

 d, a finer adjustment is made 

 by means of the screw with the 

 milled head, e, which either 

 raises or depresses the part by 

 which g is attached to the up- 

 right tube. The mirror is re- 

 presented at h, supported on 

 trunnions, and capable of mo- 

 tion upwards or downwards, so 

 as to reflect the light on the 

 object placed on the stage- 

 plate ; c ' is the diaphragm or 

 stop, or perforated plate attached to the stage, with the view of 

 shutting ofi' the extreme rays of light. The object-glass or objective 

 is placed at the lower end of the instrument, /, and the eye-piece or 

 ocular at the upper part, h. 



In fig. 951 a diagram is given to explain the mode in which the 

 compound microscope acts. In this figure, o is the object, above 

 which is seen the triple achromatic object-glass or objective, consisting 

 of three achromatic lenses, which are combined in one tube ; c c is the 

 eye-piece or ocular, consisting of two plano-convex lenses, one at e, 

 being the eye-glass, and the other at c, the field-glass. Three rays of 



Fig. 950, Smitli and- Beck's compound microscope for students. A, brass stand, sup- 

 ported on three feet ; 6, mirror supported on trunnions ; c, diaphragm ; d, stage-plate on 

 which the ohject is placed ; e, screw with milled head for fine adjustment ; g, brass tube in 

 which the body of the instrament is moved, so as to effect the coarse adjustment ; /, the 

 object-glass or objective; %, the eye-piece or ocular. Fig. 951, Diagram to show the 

 mode in which the compound microscope acts. O, an object, with three rays of light from 

 its centre, and three from each of its ends ; e c, eye-piece, consisting of two plano-convex 

 lenses — one at e, the eye-glass, the other at c, the field-glass ; &, diaphragm ; a, the point 

 where an image would be formed if the rays were not made to converge by the lens c. 



Hg, 960, 



Fig, 951. 



