52 



MAGNIFICA TION AND DRA WING. 



tacks, or in some other way. (B) The lines made while using the 

 camera lucida should be very light, as they are liable to be irregular. 

 (C) Only outlines are drawn and parts located with a camera lucida. 

 Details are put in free-hand. (D) It is sometimes desirable to draw the 

 outline of an object with a moderate power and add the details with a 

 higher power. If this is done it should always be clearly stated. It is 

 advisable to do this only with objects in which the same structure is 

 many times duplicated, as a nerve or a muscle. In such an object all 

 the different structures could be shown, and by omitting some of the 

 fibers the others could be made plainer without an undesirable enlarge- 

 ment of the entire figure. 



(E) If a drawing of a given size is desired and it cannot be obtained 

 by any combination of oculars, objectives and lengths of the body of 

 the microscope, the distance between the camera lucida and the table 

 may be increased or diminished until the image is of the desired size. 

 The image of a few spaces of the micrometer, will give the scale of en- 

 largement, or the power may be determined for the special case (§ 127). 



(F) It is of the greatest advantage, as suggested by Heinsius (Zeit. 

 w. Mikr., 1S89, p. 367), to have the camera lucida hinged so that the 

 prism may be turned off the ocular for a moment's glance at the pre- 

 paration, and then returned in place without the necessity of loosening 

 screws and readjusting the camera. This form is now made by Zeiss, 

 but as yet no quadrant is added. Any skilled mechanic can add that, 

 however. 



[(B. 31, 355), (Beh. no), (C. 112), (Fol. 70), (Frey 38), (J. R. M. S. 

 1883, pp. 283, 560 ; 1886, 516 ; 1888, pp. 113, 809, 798) ; (Amer. M. M. 

 Jour., 1888, p. 103; 1890, p. 94); (Z. w. M. 1884, p. 1-21 ; 1889, p. 



367)]- 

 § 127. Magnification of the Microscope and Size of Drawings 



with the Abbe Camera Lucida. — In determining the standard dis- 

 tance of 250 millimeters at which to measure the image in getting the 

 magnification of the microscope, it is necessary to measure from the 

 point marked P on the 'prism (Fig. 30) to the axis of the mirror and 

 then vertically to the drawing board. 



In getting the scale at which a drawing is enlarged the best way is to 

 remove the preparation and put in its place a 1 stage micrometer, and to 

 trace a few (5 or 10) of its lines under one corner of the drawing. The 

 value of the spaces of the micrometer being given, thus, 



-j-j^th mm. 

 The enlargement of the figure can then, be accurately determined at 

 any time by measuring with a steel scale the length of the image of 

 the micrometer spaces and dividing it by their known width. 



