n 



constructed with a special view to avoid this diffi- 

 culty. They are all, however, considerably more 

 expensive, but should be procured if means will 

 permit. 



The procedure of working should be about as fol- 

 lows : Focus upon the object and then incline the 

 body, so that the center of the eye-lens will be 10 

 inches from the table. To obviate repeated measure- 

 ments, a standard stick of this length may be used. 

 If the instrument is so low that it will not allow the 

 inclination of the body to an angle of at least 45 

 degrees when at this distance, it should be placed 

 upon a box ; or, if not too high, upon the case of the 

 microscope. Now readjust the mirror and attach the 

 camera lucida from below and place the paper under 

 the instrument ; look into the camera lucida from 

 above, being careful that the eye is directly over the 

 center of its opening, and the image will be found to 

 be projected upon the paper. Possibly, and very 

 probably, it will appear faint. This is due to the fact 

 that the paper is almost as highly illuminated as the 

 field. To remedy this defect a cardboard should be 

 placed between the paper and light, so that the former 

 will be shaded ; the object will now come out in 

 strong contrast. Take a well pointed pencil and fol- 

 low the lines in the image. A little difficulty may at 

 first be experienced in seeing both the pencil and 

 image at one time, but after a little practice this is 

 overcome. 



