84 THE MICROSCOPE. 



ing of an object brought into the axis of the microscope 

 is not disturbed by it ; and the workmanship is so accurate 

 that the stage may be driven through its whole revolution 

 without throwing out of the field an object viewed with 

 the i^g- th objective. The stage withal is made thin enough 

 to admit of the most oblique light being thrown on the 

 object, such as that obtained by the use of the Amici 

 prism, as shown arranged in the preceding figure. The 

 sub-stage is also provided with rotatory, rectangular, and 

 vertical movements, and is made in such a manner as to 

 admit of the simultaneous use of the polarising prism and 

 of the achromatic condenser. 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 Lea- 

 land, such as a student's microscope, with |-inch stage 

 movement, coarse and fine adjustments to body, plane and 

 concave mirrors, revolving diaphragm, Lister's dark-wells, 

 and two eye-pieces, for the price of 81. 



An improved form of microscope (fig. 41) is manu- 

 factured by Mr. Ladd, of Beak Street, Eegent Street ; 

 having a stand so simple and light in its construction as 

 to render it very portable and useful. It is fitted with a 

 magnetic stage, which facilitates the moving of the objects 

 when placed on it by the unaided fingers; a point of some 

 importance to such microscopists as desire to retain and 

 cultivate delicacy of touch in preference to that growing 

 dependence upon mechanical movements. The main 

 features of this form of microscope are, that the bear- 

 ings for the compound body, stage, and sub-stage are all 

 fitted, while connected together into the dovetailed brass 

 bar running from top to bottom of the instrument. The 

 magnet is attached to the under part of the stage, and a 

 gilt iron bar, ledge, or keeper, serves for an object-rest 

 The sub-stage is constructed of three thin plates having 

 rectangular movements, the top one having a tube attached, 

 into which is fitted the Polariscope, spotted lens, &c, the 

 focussing of which is by a rack placed below. The mirror, 

 being provided with a double-jointed arm, can be used 

 vrith any amount of obliquity. The stand forms a tripod 



