92 



THE MICROSCOPE. 



the stage, and to this carriage a rotatory motion is 

 given by a milled-head, the amount of the movement, 

 which may be carried through an entire revolution, 

 being exactly measured by the graduation of a circle 

 of gun metal, which is borne on the upper surface 

 of the ring. The rotatory action of the stage being 

 effected beneath the traversing movement, the centring 

 of an object brought into the axis of the microscope is 

 not disturbed by it ; and the workmanship is so accu- 



FIG. 48. Poicell and Zealand's Microscope arranged for direct illumination. 



A. Secondary Stage racked up to bring the Achromatic Condenser close to 

 the object. 



rate that the stage may be driven through its whole 

 revolution without throwing out of the field an object 

 viewed with the T Vth objective. The stage withal is 

 made thin enough to admit of the most oblique light 

 being thrown on the object. This instrument combines 

 remarkable steadiness with great solidity, and is so 

 well balanced on its horizontal axis that it requires no 

 clamping in whatever position it may be placed. 



Cheaper instruments are furnished by Powell and 

 Lealand ; a student's microscope, with |^-inch stage 



