ZOOLO&Y AND BOTANY, MIOROSOOPY, ETC. 131 



observation, and during the taking of the picture to allow a momentary 

 entrance of direct snnlight; while that of B is to throw, during the 

 observation, the light from the object by means of a totally reflecting 

 prism into a second tube through which the image can be observed ; at 

 the moment of exposure the prism moves to one side, and permits light 

 from the object to enter the camera. 



The shutter A, fig. 25, consists of a slide, 5J-6 cm. broad and about 

 15 cm, long, working between grooves in a wooden or metal frame, and 

 movable by a spiral spring s, the tension of which is regulated by the 

 screw m. At one side of the slide is a circular or square aperture, over 

 which a smoked or opalescent glass can be placed. Beyond the aperture 

 is an open space of variable breadth of 1-2 cm. Before the slide is 

 released the aperture is in front of a corresponding circular opening of 

 4-5 cm. diameter in the frame. The release of the slide takes place pneu- 

 matically by the knob of the cylinder c raising the spring with the catch r. 

 This slide is placed behind the diaphragm opening of the Microscope in 

 such a way that the middle-point of the opening in the frame is on the 

 optic axis. The shutter B, fig. 26, provided with brass tubes for con- 

 necting it with camera and Microscope, consists of a metal box containing 

 a totally reflecting prism which, during the observation, directs the ligit 

 from the object into the side tube t, and at the same time closes the 

 opening behind leading to the camera. The prism is fixed to a movable 

 slide which is under the tension of the spring s, with screw m; on 

 releasing it pneumatically, the slide carrying the prism moves to one 

 side and allows light to pass from the tube to the camera. 



In order to allow of observation with the eye-piece for diflferent 

 positions of the camera, the author makes the two lenses composing the 

 eye-piece movable, so that the distance between them can be varied 

 within certain limits ; the images thus obtained are not quite plane, and 

 have coloured edges, but are otherwise sufficiently well defined. 



The two shutters are released together by means of two tubes joined 

 by a three-way piece to a caoutchouc ball. Care must be taken, how- 

 ever, that the shutter B works somewhat quicker or is released sooner 

 than A, so that the light-path to the camera is open during the illu- 

 mination of the object as the open space / in A passes in front of the 

 opening in the frame. This is easily effected for equal tension of the 

 two springs by using a three-way cock instead of merely a three-way 

 piece, and placing the cock in a definite position. 



To avoid shaking the whole apparatus, the two shutters are mounted, 

 as seen in fig. 24, on a single separate stand. The shutter B is 

 connected with the camera by Zeiss's method. Somewhat large moving 

 objects (e. g. Daphnida) are placed in cells which just leave room for 

 movement between the two sides. 



Sunlight rendered monochromatic by ammonio-copper oxide or 

 Fehling's solution is the light employed for the adjustment. When 

 the objects move too fast for successful adjustment, observation is made 

 of an air-bubble in the cell. 



To increase the illumination during the exposure, a condensing 

 lens L of large opening (10 cm.) is inserted in such a position 

 that the object is at its focus, or, if the field of view of the objective is 

 greater than the surface thus illuminated, so that the object is in the 

 converging part of the beam. If, however, the object surface to be 

 illuminated is smaller (by use of a stronger objective), a condenser can 



K 2 



