THE MICROSCOPE. 



523 



require much time and labour, a good microscope is an expensive 

 instrument, which should only be purchased if required for real 



FIG. 285 (^ real size, C an. proj.}. 



investigations, such as are undertaken by the botanist, physiolo- 

 gist, &c. 



The principle of the microscope may be fully demonstrated by 

 means of two lenses, of 3 and 5 cm focal length. Get a cork which 

 is about 3 cm thick ; cut two round discs, each l cm in thickness ; bore 

 holes in the middle of each and widen them with the rat tail, so 

 that the lenses will go into the aperture when moderate pressure is 

 applied. Before the lenses are inserted, a small portion of the edge 

 of each cork ring is filed away, so as to produce a flat surface ; care 

 should also be taken not to place the lenses in an oblique position 

 into the frames. In fig. 285 A is a front view cf the larger lens 

 with the ring, B is a section of the same. Both rings with the 

 lenses are then glued upon a small board, I5 cm long and 3 cm broad ; 

 the lens of 5 cm focal length, the eye-piece, at one end, and the other 

 lens, the object-glass, at the opposite end, leaving a space of ll cm 

 between them. A common cork is glued to the under side of the 

 board, so that the whole may be clamped in the fork of the retort- 

 stand, as shown in fig. 265 C. Two cork discs, a and I, have an in- 

 cision made across one of their flat sides : into one of these a piece of 

 stiff writing paper may be stuck, and into the other a piece of sheet 



