ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 543 



focusing screens, one of ground glass and the other of clear plate glass, 

 are supplied with the apparatus, together with two single dark-slides 

 taking plates 24 cm. square, with carriers for smaller sizes, either English 

 or Continental. The front of the camera is fitted with a pneumatic 

 shutter for time and instantaneous exposures, and for the light-tight 

 connexion referred to above, into which the objective-adapters can be 

 pushed. 



The other half of the optical bench is occupied by (1) the Micro- 

 scope mounted upon a sliding base-plate ; (2) an illuminating lens or con- 

 denser ; (8) a large iris-diaphragm ; and (4) a Liliput arc-lamp. Each 

 of these accessories is adjustable for height ; that for the sliding base- 

 plate being controlled by a hand-wheel below the level of the steel rods, 

 this adjustment being necessary to compensate for the variation in the 

 heights of the optic axis of horizontal Microscopes. A special me- 

 chanism is fitted to the base-plate, and this, in conjunction with a 

 lengthening rod, permits of the fine-adjustment being effected during 

 observation of the image on the screen. 



For taking photographs of large objects with the microsummars 

 without the Microscope, a special vertical stage is provided, mounted on 

 a sliding carrier, and fitted with a micrometer-screw fine-adjustment, to 

 which the lengthening rod referred to above can also be connected should 

 the length of the camera necessitate its use. A series of interchangeable 

 diaphragms is supplied with the stage, and the diameter of each dia- 

 phragm corresponds approximately to the focal distance of the lens with 

 which it is to be used, each diaphragm being provided with an illuminat- 

 ing lens which will illuminate uniformly and without colour the given 

 aperture. Objectives and diaphragms are marked, so that the correct 

 pair can be rapidly selected. 



Leitz' Photomicrographic Apparatus for Photographing Insects.* 

 This apparatus (fig. 65) has been suggested by Hermann, and is num- 

 bered III. in Messrs. Leitz' Catalogue. It is constructed for use in the 

 horizontal position only, and is mounted on a stand consisting of two 

 steel tubes resting upon two pairs of cast-iron feet. The camera, 

 which can be extended to 70 cm., is mounted upon steel tubes ; it 

 has wire supports to prevent sagging, and the bellows-frame can be 

 retracted in the same manner. The front carrying the objectives is 

 fitted with a time and instantaneous shutter. Two lamps (Liliput arc, 

 or incandescent gas) with condensing lenses serve to illuminate the ob- 

 ject. These lamps are mounted on slotted arms attached to the pillars 

 carrying the camera front in such a manner that not only the distance 

 of the illuminant, but also the angle of incidence of the light can be 

 varied within wide limits ; it thus becomes an easy matter to illuminate 

 an object brightly and uniformly, or to control the density and position 

 of the shadow required to give the necessary contrast. 



The object-holder consists of a base-plate sliding upon the tubular 

 base, to which it can be clamped in any desired position by means of 

 a thumb-screw. It has two micrometer-screw adjustments for moving 

 the object in a horizontal plane in two directions, at right angles to one 



* Leitz' Catalogue, 43 G, Photomicrographic Apparatus, pp. 16-18. 



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