202 



USE OF THE MICROSCOPE, 



II 



11 

 |l 



ll 



Fig. 130. 



colours, such as green, red, and even white ; but It will be 

 found by far the best plan to use a dead black, as then there 

 is no danger of the definition being interfered 

 with by light reflected from other parts than 

 from the object itself. When the subject of 

 investigation is in fluid, and of a white coloiu', 

 a portion of black paper may be placed be- 

 neath it, to form a backgroimd; if the paper 

 be made with lampblack, there is no fear of 

 the colouring matter coming off; or even a 

 piece of glass which has been blackened on 

 one side with sealing-wax, dissolved in spirits 

 of wine, will form an excellent background, 

 and such a thing should be always at hand, 

 it wUl often be found convenient, and wUl 

 answer the purpose of the black circular disc 

 with which all the old microscopes were sup- 

 pHed. The method of using the dark stops 

 is shown in fig. 131, where a represents the 

 end of the compound body, b the 

 object-glass, c the Lieberkuhn, e the 

 dark stop, which is to be placed in 

 the hole of a small arm, that is capa- 

 ble of being turned under the stage 

 after the diaphragm has been re- 

 moved, / a pair of forceps, in which 

 is held the object, d. The rays re- 

 flected in nearly parallel lines from 

 the mirror are by the Lieberkuhn 

 concentrated on the object, and those 

 which are near the centre are pre- 

 vented from passing into the object- 

 glass by the dark stop, e: it little matters how small the 

 object is, or whether it be transparent or not, as the dark 

 stop wiU entirely prevent any hght passing either through or 

 around it. 



When the side-reflector and the Lieberkuhn are compared 

 together, it wUl be seen that, with the latter, all opaque 



Fig. 131. 



