APPENDIX 



I. The Compound Microscope (Fig. 230). — This consists essenti- 

 ally of a stand which has for its purpose the appropriate support 

 and adjustment of the optical parts. The latter comprise two 

 systems of lenses, known respectively as ocular [Oc.) and objective 

 [Ob.), whilst accessory structures are constituted b}' a mirror (M.) 

 for reflecting light, and, in better instruments, a condenser {Co.) 

 for concentrating light upon the object. 



The stand consists of a heavy /oo^ or base {Fa.), bearing 

 a rigid upright pillar (L.). To the latter the remaining por- 

 tions of the microscope are hinged in such a way that the whole 

 can be employed either in a vertical or in an inclined position. 

 The part actually hinged to the piUar is known as the limb, 

 and to this the flat stage (S.) is attached, at right-angles, at the 

 lower end, and the body tube (T.) towards the upper end. The 

 stage, which is usually square, is perforated by a central aperture 

 through which the light from the mirror reaches the object. In 

 transferring the microscope from place to place, it should always 

 be carried by the non-movable parts. 



The body tube is a hollow cylinder, usually of brass, and is 

 adapted to take the ocular or eyepiece [Oc.) at its upper, and 

 the objectives (Ob.) at its lower, end. In order to secure rapid 

 change of magnification, a nosepiece {N.), bearing two or three 

 objectives, is screwed into the lower end of the body tube ; by 

 simply turning this a different objective can be brought to bear 

 on the object. The distance between eyepiece and objective 

 can be increased or decreased by pulling out or pushing in the 

 draw-tube {D.t.), which is fitted into the upper end of the body 

 tube. In order to focus the object clearly, the entire system of 

 lenses can be moved nearer to, or farther from, the stage by means 

 either of the coarse or fine adjustments. The coarse adjustment 



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