LESSON IV. 



MEASUREMENT OF OBJECTS UNDER THE 

 MICROSCOPE. 



1. Schrb'der's compound camera lucida. This 

 is perhaps one of the easiest to use if the microscope 

 can be tilted. Set the microscope to an angle of about 

 45. Focus with a low power the lines of a stage 

 micrometer, i.e. a millimetre divided on glass into tenths, 

 and one of the tenths into hundredths. 



Place the drawing paper on the table in front of 

 the microscope ; put the camera over the ocular, move 

 the point of a needle on the drawing paper, the point 

 will be seen through the camera. Then move the 

 camera slowly down till the lines of the stage micro- 

 meter, as well as the point of the needle, are distinct. 

 Focus with the fine adjustment if necessary, and 

 continue as in 3. 



2. Zeiss' drawing prism (camera lucida) (Fig. 

 2). Place a drawing-board (made so that the drawing 

 surface is at an angle of 25 with the table) in front 

 of the microscope, and touching its foot, or at an 



