CH. V.] 



DRA WING WITH THE MICROSCOPE. 



115 



known angle in a moment, then the drawing board can be hinged and 

 the elevation of io° and 20 determined with a protractor. The draw- 

 ing board is very conveniently held up by a broad wedge. By marking 

 the position of the wedge for io° and 20 the protractor need be used 

 but once, then the wedge may be put into position at any time for the 

 proper elevation. 



§ 175. Abbe Camera and Inclined Microscope. — It is very fatigu- 

 ing to draw continuously with a vertical microscope, and many 

 mounted objects admit of an inclination of the microscope, when one 

 can sit and work in a more comfortable position. The Abbe camera is 

 as perfectly adapted to use with an inclined as with a vertical micro- 

 scope. All that is requisite is to be sure that the fundamental law is 

 observed regarding the axial ray of the image and the drawing surface, 

 viz., that they should be at right angles. This is very easily accom- 

 plished as follows : The drawing board is raised toward the microscope 

 twice as many degrees as the mirror is depressed below 45 ° (§ 174), 

 then it is raised exactly as many degrees as the microscope is inclined, 

 and in the same direction, that is, so the end of the drawing board shall 

 be in a plane parallel with the stage of the microscope. The mirror 

 must have its edges in planes parallel with the edges of the drawing 

 board also (Fig. no). 



Fig. 1 10. Arrangement of the 

 drawing board for using the mi- 

 croscope in an inclined position 

 with the Abbe camera lucida {de- 

 signed by Mrs. S. P. Gage). 



A very elaborate and convenient drawing board has been devised \>y 

 Bernhard (Zeit. wiss. Mikroskopie, Vol. XI, (1894) p. 298), whereby 

 the proper inclination can be given the drawing board for the vertical 

 microscope and also for an inclined microscope. The drawing surface 

 as a whole can be raised or lowered to meet the needs of different ob- 

 jects. Fig. in shows an excellent drawing board after the Bernhard 

 form. 



§ 176. Drawing with the Abbe Camera Lucida. — (A) The light 

 from the microscope and from the drawing surface should be of nearly 

 equal intensity, so that the image and the drawing pencil can be seen 

 with about equal distinctness,. This may be accomplished with very- 



