116 SUMMARY OF CURRENT RESEARCHES RELATING TO 



horizontal or a vertical position ; in the former, the iron frame to which 

 it is attached is fixed upon a tahle, using an inclining Microscopo ; in 

 the latter the instrument is supported as shown in tho figure upon an 

 iron stand, which runs upon wheels, but can be fixed in any position by 

 means of tho three screws F. The apparatus consists of two parts, the 

 Microscopo and tho camera ; V is tho focusing screen, upon which tho 

 image is focused by means of tho rod b b u terminating in a toothed 

 wheel 6„ which works into a similar but larger toothed wheel E, 

 occupying the place of tho usual micrometer-screw. B is the light- 

 proof connection between the camera and Microscope, and consists of 

 a leather bag fixed to the Microscopo by the ring r. The camera 

 consists of the three mahogany frames Kj K 2 K 3 , united by the leather 

 bellows Bj B 2 , which can be extended to the length of a metre ; tho 

 focusing screen can be rotated about an axis A, perpendicular to the axis 

 of the instrument, a is a screw spindle, placed close to b, by means of 

 which the camera may be clamped in any desired position to its iron 

 standard. "When the apparatus is used in the vertical position the 

 Microscope simply stands upon its iron base, and is fixed below the 

 camera by means of a screw-clamp Sc^, which grips its horseshoe stand. 

 The size of the plates used with this apparatus is 15 X 15 cm. 



Fig. 20 represents the similar instrument of Herr M. Stenglein, 

 which carries its own illuminating apparatus. For this purpose the 

 height of the instrument is considerably increased ; a space of 66 cm. at 

 the lower end of the standard serves to carry the movable parts which 

 constitute the illuminating apparatus, namely a plane mirror 20 cm. 

 square Sp, a condenser of 10 cm. radius and 21 cm. focal length L, a 

 light-filter C, to secure monochromatic light, consisting of a vessel filled 

 with ammoniacal solution of copper oxide, and Abbe's illuminator ; to 

 these may also be added, if necessary, a diaphragm B, which is to be 

 employed when electric light is used, and in this case the mirror is 

 replaced by the electric lamp. To preserve the centering, the illumi- 

 nator and the Microscope not only slide along the upright, but are 

 provided with a slight lateral adjustment, and the apparatus is cen- 

 tered by using the smallest diaphragm of the Abbe illuminator and 

 a diaphragm of equal size, which is made to be attached to the con- 

 denser. • 



Stegemann's Photomicrographic Camera. — The instrument repre- 

 sented in fig. 21, and devised by Herr A. Stegemann, corrects, it is 

 claimed, a defect of the ordinary apparatus by supplying the means of 

 adjusting the distance between the objective and the focusing screen, 

 upon which depends tho relative size of the photographic image, and by 

 measuring this distance upon a fixed scale. A square pillar rising from 

 an iron foot carries the camera, with the objective-frame and the focusing 

 screen which slide upon it ; the pillar is graduated, and by means of a 

 vernier attached to the adjustment-screw of the camera gives the exact 

 distance between objective and focusing screen. The apparatus can be 

 used either to photograph objects in their natural size, in which case the 

 object is placed on a glass plate fixed to the foot ; or with the Microscope, 

 which is then placed in the forked support which serves to carry the 

 glass plate. 



In this instrument the stratum of liquid which is used as a light- 

 filter for monochromatic light is contained in a vessel which slides into 



