THE COMPOUND MICROSCOPE 



all microscopic work. At the top of the foot there 

 is a joint, in order that all the other parts of the 

 stand may be inclined at any angle, from the vertical 

 to the horizontal. Just above the joint is a bent 

 arm of brass, to the forward end of which a brass 

 tube is affixed. This tube is designed to hold the 

 lenses, the objective at its lower end, the eyepiece 

 at its upper end. The tube is always blackened 

 inside ; were this not the case, light passing through 

 the objective would be reflected in all directions 

 from the sides of the tube and a clear image of the 

 object could never be obtained. The tubes of micro- 

 scopes vary in length according to their country of 

 origin; English and American tubes are ten inches 

 long, those of continental make vary from a little 

 more than six inches to rather more than seven 

 inches in length. 



Affixed to the lower end of the bent arm of brass, 

 mentioned above, is a flat metal plate, known as 

 the stage; at its centre, there is a circular hole 

 through which rays of light pass to illuminate objects 

 placed upon it. Below the stage, at the edge nearest 

 to the foot, there is a metal peg, over which fits 

 a tube to which a mirror is attached by a moveable 

 joint. The mirror reflects light rays through the 

 opening in the stage. The tube, holding it, can be 

 slipped up and down the peg under the stage, 

 thereby bringing it nearer to or further from the 

 object and so altering the intensity of the reflected 

 light, as we shall explain in a moment. Owing to 

 its moveable joint, it is possible to swing the mirror 



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