ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



517 



(see below) E ; J and K adjustable carriers for the camera ; Z exposure 

 shutter ; S c h draw-off slide of the dark slide shutter ; G handle of the 

 frame for inserting the photographic plate. The " finder " is for per- 

 sonal observation and for adjustment, and is applied over the ocular of 

 the Microscope. It is a specially constructed auxiliary, whereby the 

 image can be thrown on to a fluorescent plate and observed through a 

 strong loup. When the image is sharply defined on the fluorescent plate 

 it will be also sharply defined on the photographic plate after the finder 

 has been replaced by the camera. The plate must be set up 30 cm. 

 from the ocular cap. Variations, not exceeding a few centimetres, of 



Fig. 112. 



the camera-length do not much affect the sharpness of the image. The 

 spark discharge between cadmium electrodes (in certain cases mag- 

 nesium electrodes) of a Leyden jar, worked by an induction machine, 

 serves as a light-source. The spark-length should be about 10 cm. The 

 spark-light is led through a special illumination apparatus of rock- 

 crystal lenses and prisms, and the light of wave-length 275/a/x (if «»f 

 magnesium 280 /a/a) is separated off by an iris diaphragm. This dia- 

 phragm forms the entrance-pupil of a rock-crystal condenser, which 

 takes the place of the ordinary glass condenser. The light then passes, 

 as a cone of larger or smaller aperture, to the object. In fig. Ill then' 

 is shown the stage-plate with the illuminating apparatus, one-fifth full 

 size. F is the spark-stand ; Kj the collimator ; P x P 2 the rock-crystal 

 prisms for conducting the rays of various wave-lengths from the light- 

 source F ; K 2 the collector, which gathers the rays of a certain wave- 



