ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



941 



Figs. 213 A^-D 214. 



the side, the plate A A must also be inclined to the axis of the Micro- 

 scope, and the body B of the camera be placed as near as possible to 

 the eye-piece. 



Having made the adjustment approximately according to these 

 directions, on looking down the Microscope and keeping the pupil of 

 the eye exactly over the edge of the prism, there is seen within the field 

 of view, and simultaneously with 

 the microscopic image, a portion of 

 the surface of the table, that part 

 which lies near the foot of the in- 

 strument on the side of the prism B. 

 If the camera has been put on with 

 B to the right of the observer, the 

 space which becomes visible is to 

 the right of the Microscope ; but if 

 the camera is turned towards the 

 front, as may be done when the light 

 falls on the Microscope from one side, 

 the space in front of the instrument 

 will be projected into the field of 

 view. Upon that part of the table 

 which thus becomes visible must 

 now be placed the drawing-paper in 

 such a manner that it rests upon 

 a support inclined towards the 

 Microscope about 15^ to 20^, so 

 that the plane of the paper lies 

 approximately parallel to the plate 

 A A of the camera. If, after the 

 camera has been adjusted as above 

 directed, the field of view, on look- 

 ing down the Microscope, appears 

 obscured on either side by a glare 

 of colour ; or if the drawing sui'face 

 is only visible in a part of the field 

 of view, the imperfection may be 

 cured by turning the camera very slightly round the vertical or 

 horizontal pin, testing it in one or other direction whilst looking 

 through it. 



Tighlmanii's Cylinder-Diaphragms for the Vertical Illuminator. 

 — The vertical illuminator is shown in Fig. 215 (actual size) with 

 Mr. Tighlmann's cylinder-diaphragm. The diaphragm consists of a 

 short piece of cylindrical tube, from which about one-third of the 

 circle is cut out, made to slide at will as an outer jacket over the 

 circular aperture through which the illuminating rays pass to the plate 

 of glass which is adjusted (within the adapter) in the optic axis and 

 inclined 45° so as to reflect the rays to the objective from above — 

 the objective thus serving as illuminating lens. The square end of 

 the sliding cylinder, passing variously over the circular aperture, 

 cuts off larger or smaller segments of the opening either vertically 



