107 



tance between eyepiece and table, it being- appar- 

 ent that as the distance becomes greater the 

 magnification will proportionately increase. The 

 usual standard for distance is 10 inches, although 

 this may be varied to suit requirements. Attach 

 the camera lucida ; place the paper upon the 

 table and fasten with drawing tacks ; apply the 

 eye to camera lucida ; refocus carefully with the 

 fine adjustment and endeavor to obtain equally 

 sharp view of image and pencil point. In these 

 two forms it is quite difficult to see the pencil 

 point clearly and some care will be required in 

 modifying the light or shading the paper so that 

 the image and pencil point may be sufficiently dis- 

 tinct at the same time to follow the outlines. 



In the Abbe camera lucida the optical results are 

 considerably better, since a direct view of the 

 image is obtained and the equalization of illumina- 

 tion is easily accomplished. 



While with it, the microscope is intended to be 

 used in an upright position, the reflecting mirror 

 is close to the eye so that, if the image is projected 

 vertically, a portion of the field is cut off by the 

 stage or base of the microscope and if the mirror 

 is so inclined as to bring the full field upon the 

 paper, it will not be round, but elongated or ellipti- 

 cal and thus also elongate the image. This can 

 only be corrected by correspondingly raising one 

 end of the drawing board so that it shall be at 



