THE MICROSCOPE AND ITS ACCESSORIES. 



succeed in delineating their preparations when they have given the 

 matter a fair trial. 



(B.) Various Forms of Camera Lucida. Sometimes, however, 

 a drawing has to be done to scale, or its outlines and detail* 

 accurately portrayed. There are many 

 devices for this purpose. Some ot 

 these instruments are by no means 

 easy to work with, but they are 

 excellent for tracing the outlines of 

 objects and showing the exact rela- 

 tion of one part to another, and the 

 relative size of the parts of an object. 



(i.) Zeiss's Camera Lucida (fig. 

 17). A collar (c) with a vertical rod 

 attached (a), carrying a bar (^) which 

 bears the prism or camera (K). The 

 collar is slipped over the tube of the 

 microscope and the eye-piece inserted. 

 Focus the object, and rotate the prism FIG. 17. Zeiss's Camera Lucida. (c.) 



until it i -ibnvo tho PVP niopo t,hr> collar; (a.) and (6.) supporting 



eye-pic ^ , l barg . ^ K ^ camera. 



prism covers one-half of the latter. 



The drawing-board is inclined at an angle of 20, and in looking 

 down the microscope the paper and the image of the object are 

 seen simultaneously. 



(ii.) Camera Lucida (Abbe). This apparatus is made by Zeiss 

 (fig. 1 8). The apparatus is screwed to the tube of the microscope. 



FIG. iS. Abbe's Camera Lucida. (Sp.) mirror ; (IF.) line of reflected light ; (/.) collar for 

 screwing over eye-piece ; (0.) light to eye of observer ; (>) light reflected on paper. 



The direction and reflection of the rays from the object and those 

 from the paper are shown in the figure. In all camera-lucida 

 drawings it is important to regulate the brightness of the illumination 



B 



