ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



1011 



The aquarium consists of a stand with a frame which carries the 

 aquarium proper, 10 cm. in breadth and height, and 10 mm. in thickness ; 

 this may be rej^laced by others. The frame is made of brass lacquered 

 black. The aquarium itself consists of a horseshoe-shaped piece of glass, 

 both sides of which are closed by plates of cover-glass leaving the upper 

 end open. It is thus possible to observe an organism upon either of the 



Fm. 23.5. 



two thin sides with an objective giving a linear amplification of 200-300. 

 To screen off the superfluous light and the numerous reflections in the 

 aquarium, the frame carries a diaphragm arrangement which can be applied 

 on either side at pleasure. This consists of a sliding-plate which moves 

 in two horizontal guides ; it is divided into three parts, and has an oblong 

 opening in one of the divisions. In this opening a thin plate slides and can 

 be clamped at any point. In this plate again is a circular aperture, which 

 can be closed to a greater or less extent by various diaphragms kept in 

 position by a small spring. 



If an animal is on the upper left-hand corner of the side turned 

 towards the Microscope, the sliding-plate is first moved so that the vertical 

 longitudinal opening lies in the left-hand third, the small plate is then 

 set so that its opening lies in the upper third. If, on the other hand, the 

 animal is on the right-hand side, the larger sliding-plate is moved so 

 that the longitudinal opening lies on the right, and if the animal is towards 

 the bottom, the small slide with its opening is moved downwards. The 

 two sliding-plates are now so directed that light may be thrown by the 

 mirror through the aquarium and upon the animal on the front side. The 

 aperture can be further reduced by diaphragms. 



The mirror is concave, 10 cm. in diameter, and fixed upon its stand with 

 a ball-and-socket joint so that it can be adjusted in any position. 



