264 THE USE OF THE MICROSCOPE 



38. Adjusting the Abbe Camera. — Use an eyepiece 

 with a fairly high eyepoint, preferably a compensating 

 eyepiece. Removing the eyepiece, fit on the camera sleeve. 

 Replace the eyepiece, and center the eyepiece circle in the 

 hole in the silver layer, using a 10-times magnifier for this. 

 Then alter the height of the Abbe cube over the eyepiece 

 until the eyepiece circle does not show parallactic shifting 

 when the eye and the magnifier are moved to one side. 

 Put the mirror of the camera at 45 degrees. Adjust the 

 drawing paper to the same slant as the microscope stage. 

 Adjust the light through the microscope and the light from 

 the paper until they are so proportioned that the pencil 

 point is seen with maximum clearness, as well as the micro- 

 scopical image. Distance spectacles should be used. 

 (Zeiss.) 



39. Measuring Microscopic Objects. — (a) Take a mi- 

 crometer eyepiece with the diaphragm below, such as K 20 

 of Zeiss. Put the eyepiece micrometer scale in its place 

 right side up, and focus it with distance vision. Calibrate 

 it for the objective used by comparison with a stage (object) 

 micrometer scale. The tube length must be unaltered 

 throughout the series of measurements. Any slight altera- 

 tion of tube length, or change of correction collar, requires 

 a new calibration; as does the replacement of one objective 

 by another of the same nominal focal length. Measure- 

 ment with the eyepiece scale is the best method if many 

 small objects have to be measured, such as pollen grains. 

 (6) Draw the object with the Abbe camera. Then replace 

 the slide by an object micrometer scale (of about the same 

 thickness as the slide). Draw a few divisions of this scale, 

 with the same objective, the same eyepiece and the same 

 positions of camera and drawing paper. Use the drawn 

 scale to measure the drawing of the object. This is prob- 

 ably the best method when only a few objects in a field, 

 such as chromosomes, are to be measured. 



40. Measuring Magnifying Power of Objectives.— Take 

 the micrometer eyepiece scale used in 39. Take out the 

 scale and measure its length under a lens. Then its degrees 



