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SUMMARY OF CURRENT RESEARCHES RELATING TO 



attained in the disposition of the pillar and foot. The curving of the 

 upper pillar affords a good grip for the Microscope and provides ample 

 room for a large object-stage. In place of the usual mechanism of 

 screws, levers, or inclined planes, a principle, apparently novel as regards 

 the Microscope, has been adopted for the attainment of a fine adjust- 

 ment : a disc (/, fig. 153) rotates about a strong axis and is bounded by a 

 curved surface excentrically placed with regard to the axis : this disc 

 raises the tube the desired distance. Fig. 153 is a vertical section 

 through the mechanism of the micrometer adjustment. The periphery 

 of the disc is made of two equal spirals which are placed together in a 



Fig. 153. 



heart-shaped manner, thus forming a kind of cam. The spiral starts 

 from the indent of the cam (i.e. the point nearest the rotation-centre) 

 up to its apex : the range is about 3 mm., and the disc simultaneously 

 travels an equal amount. A support Jc is placed on this spiral by 

 means of the roller g ; it shares in the movement and communicates it 

 to the tube. The heart-shaped piece is rigidly connected with a toothed 

 wheel d, which engages on two sides in the thread of an endless screw a. 

 This double engagement of the teeth and axle is clearly seen in fig. 

 154. This endless screw is operated by a pair of milled heads placed 

 under the milled heads of the coarse adjustment. The position b of the 



