MICROSCOPY. 



521 



reflectors, direct vision being accomplished 

 through a hole in one of them ; and this is the 

 basis of many amateur arrangements which 

 are easy to make and excellent to use. In Mr. 

 Grunow's camera the prism is separated into 

 two, one of which, as shown in Fig. 40, reflects 

 the rays, P, from the paper horizontally to 

 the other, which turns them upward to the 

 eye at P 1ST, in conjunction with the direct rays, 

 M, from the microscope, which pass through 

 a small central aperture, about half the diame- 



Fio. 41. SCHROEDER'S CAMERA LTJCIDA. 



ter of the pupil of the eye, at o in the reflect- 

 ing silver film fg, which bisects the cubical 

 prism e Ji. When the microscope is inclined at 

 the convenient angle of 45, the drawing-field 

 is on the plane of the table, directly below the 

 ocular, the optical performance of the appara- 

 tus being as excellent as its arrangement is 

 convenient (Behrens, Am. ed., p. 118). Prof. 

 Abbe's camera differs only in substituting a 

 plane mirror for the triangular reflecting prism. 

 Dr. H. Schroeder's, the last brought out, is 

 based upon Mr. Wenham's binocular prism for 



C D of polished glass separated by a thin film 

 of air, and sufficiently inclined to give consid- 

 erable but not total reflection. Unlike the 

 other recent forms, the direct ray, J K, is re- 

 ceived from the paper, and the reflected ray, 

 H I, from the ocular, giving a very easy view 

 of the pencil, but some disadvantage in in- 

 creased distance of the eye-point K from the 

 ocular, and consequent limiting of the field of 

 view. The angular aperture, however, of the 

 cone of light at the eye- point K is about 30, 

 thus utilizing the whole field of (about) a " B " 

 ocular. This camera is used with the micro- 

 scope and drawing-field in the same position 

 as is the Grunow apparatus, which it much 

 resembles in satisfactory working qualities 

 ("A. M. M. J.,"1884, p. 221). 



Photo-micrography, as a substitute for the 

 camera lucida, in rendering microscopical im- 

 ages material and permanent, was lately a lux- 

 ury attainable by few, but has now become 

 popular through the adoption of the dry-plate 

 process in photography, the introduction of 

 the amateur camera and its outfit, and the 

 ingenuity with which several experimenters 

 have adapted such apparatus to the micro- 

 scope. By some, a simple cone slipped over 

 the upper end of the microscope-tube, with 

 a holder at the top for a sensitized plate as 

 in Stem's apparatus (" J. R. M. S.," 1882, p. 

 113), is made to do good service. Some mak- 

 ers now prepare a special " photo-micro cam- 

 era " of simple but efficient model, of which a 

 good example is the one devised by Mr. H. 

 F. Atwood ("Proc. Am. S. M.," 1884, p. 176); 

 while others furnish an ordinary amateur cam- 

 era arranged for use in connection with al- 

 most any microscope. Mr. William H. Walms- 



FIG. 42. PHOTO-MICROGRAPHIC ARRANGEMENT. 



high powers, and differs from the Nachet cam- 

 era in having the beveled edges more inclined, 

 so that the oblique axial ray H, Fig. 41, is at 

 an angle of 45 with the direct axis J K, while 

 the second reflection takes place from surfaces 



ley's apparatus, shown in Fig. 42, illustrates in 

 detail the arrangement of camera, microscope, 

 and illuminating apparatus adopted by a person 

 of experience and success in this field of labor 

 ( u Proc. Am. S. M.," 1883, p. 59). A small 



