52 



THE MICROSCOPE 



has been removed. This form has adjustable slide- holders, so 

 that slides of any length between 2 and 4 inches can be held. 





Fig. 45. — No. 3306, Rotating Mechanical Stage. 



Centring 

 rotating 

 stage. 



Glass slip. 



2J inches 



The ordinary mechanical stage is made to take only the 3-inch 

 standard length slide. It has a lateral travel of 

 (55 mm.) and a vertical travel of 1 inch (25 mm.). 



Fig. 98, page 105, shows another form of mechanical stage, in 

 which the actuating milled heads are at the side instead of 

 being vertically over the stage. It can also be removed from the 

 large square stage. It has a lateral travel of 3 inches (75 mm.) 

 and a vertical travel of \\ inches (30 mm.). 



Fig. 97, page 103, shows a plain rotating stage with two stage 

 clips and two centring screws. The centring screws are primarily 

 intended for moving the axis of rotation so as to adjust it to the 

 exact optic axis, but they may also be used as a means of adjusting 

 the position of the object to a small extent in both directions. 

 This stage has only a travel of about 1/6 inch in either direction, 

 and cannot be used for searching a specimen or for registering 

 positions on the slide. It forms a means of finally adjusting a 

 specimen that has been roughly adjusted by the fingers. 



A revolving stage is necessary for petrological work. It is 

 very useful in observing opaque objects illuminated with oblique 

 light, as the behaviour of the shadows, where the stage is rotated, 

 assists in the interpretation of the 

 structure. It is of great service in 

 adjusting an object into the correct 

 position for drawing, measuring, or 

 photomicrography. 



Holding an object for examina- 

 tion under the microscope calls for various appliances, according 

 to the nature of the object. The most universal method consists 



Fig. 46.— No. 3400, Glass Slip. 



