ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



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The lever motion is so regulated by suitable adjustment of the index J 

 (fig. 108), movable on a graduated circular disk, that it ranges between 

 1 to 35 teeth. The toothed wheels are in such relation to the pitch of 

 the screw that the movement of one tooth corresponds to 1 mm. It 

 is therefore possible to adjust the apparatus approximately for any 

 desired field of view whose diameter lies between 0*1 and 3*5 mm. 

 Thus in every complete up-and-down movement of the lever the object 

 is moved laterally almost entirely around the field. If the breadth of 



Fig. 107. 



the field is measured, the adjustment in millimetres is known, without 

 further observation, by the position of the upper sharp edge of the 

 index J. If the diameter of the field of view is unknown, it may be 

 ascertained in the following manner. An object-slide is marked in any 

 suitable way, an object-micrometer is inserted, and the mark so adjusted 

 that it is exactly at the left boundary line of the view-field. The lever H 

 is now turned forward and downwards until it reaches the pin p ; the 

 knob F, which at first was central, is moved to the right, the screw of 

 the index is loosened, and the index pushed close up to the lever H. The 

 observer now carefully draws the lever towards himself, and at the same 

 time follows in the Microscope the movement of the mark. When the 

 mark has reached the opposite verge of the view-field, the index is 

 clamped, and the range of lever-play is then accurately known. The 

 small knob F is in connection with a small spring-lever concealed by the 



