CHAPTER VI. 



USEFUL MICROSCOPE ACCESSORIES, LABORATORY 

 EQUIPMENT, WORK TABLES, RADIANTS. 



Drawing Cameras (Camera Lucidas). — It is very frequently 

 the case that sketches, relative proportions of structural details, 

 or actual measurements of component parts of preparations 

 being studied must be entered into notebooks. Free-hand draw- 

 ing is tedious, difficult, and if a sketch to scale is required, as is 

 usually the case, an exceptionally good judgment of proportion 

 is essential. To obviate these difficulties a drawing camera may 

 be employed. Although there are many types of these devices 

 upon the market, the chemist is usually restricted to those forms 



which permit employing the micro- 

 scope in a vertical position. 



The most convenient of these 

 drawing cameras are shown in Figs. 

 62 and 63. 



If, after attaching one of these 

 devices to the tube of the micro- 

 scope above the ocular, the worker 

 looks into the instrument, he is 

 able to see simultaneously both the 

 preparation and the page of the notebook. 



In the forms shown in Figs. 62 and 63, known as Abbe prism 

 camera lucidas, there is placed above the ocular a cube of glass 

 which has been cut diagonally, the surface of one-half being 

 silvered and cemented again in place, after a central oval per- 

 foration has been made through the silvered surface. This oval 

 aperture allows the image-forming rays of the microscope to reach 

 the eye while the silvered surface reflects from a mirror the image 

 of the notebook page or drawing paper. Fig. 64 shows diagram- 

 matically the path of the light rays, the dotted lines indicating 



127 



Fig. 62. Small Abbe Drawing 



Camera. 

 (Bausch & Lomb Optical Co.) 



