MR. ROUSSELET'S TANK MICROSCOPE 



269 



of the 

 upon 



referred, is carried on a jointed arm, which is clamped to the tank, 1 

 the tank being nowhere deeper than the range of focus of the lens 

 employed. The arm moves on a plane parallel to the side of the 

 tank, and the lens is focussed by means of a rack and pinion, 

 arranged upon the body 

 clamp, as seen 

 the " left-hand 

 corner of the figure. 

 The following points 

 will recommend them- 

 selves to those who are 

 in the habit of looking 

 at their captures with 

 the pocket lens in tl it- 

 ordinary way : 



When an object of 

 interest is found, it can 

 be followed with the 

 greatest ease and taken 

 up with a pipette, both 

 hands being fi ee for this 

 operation. 



It so frequently 

 happens that a minute 

 object is lost simply by removing the pocket lens for an instant to 

 take up the pipette ; in the above apparatus the lens remains in the 

 position in which it has been placed. By a new process glass tanks 

 are made with melted seams ; these cannot possibly leak, and are to 

 be preferred to those with the ordinary cemented joints. 



1 We prefer to have a stand or ' rest ' for the tank, and on one side of this a firm 

 pillar to which (and not to the side of the aquarium) the jointed arm is clamped. 

 This enables shallower and deeper tanks to be employed without shifting the rack 

 carrying the lens. 



FIG. 211. Rousselet's aquarium microscope. 



