\ 



1857.] The Microscope. 277 



visible as a whole, and may perhaps lay his finger upon the stage 

 hoping to see it wonderfully enlarged, whereas with even a moder- 

 ate power, a single minute, marking upon its surface, is more than 

 sufiicient to fill the whole field of view. An instrument to reduce 

 the thickness of minute objects, and flatten all their parts down to 

 the same plane, is a very necessary adjunct to a microscope ; and is 

 named the compressorium. 



Many other adjuncts are required by the working microseopist ; 

 the illuminating apparatus especially is very important, and requires 

 great skill in adjusting, and managing it with the higher powers. — 

 Here is where the novice will encounter the greatest difficulty. — - 

 However excellent all the other parts may be, vision will be imper- 

 fect unless the right quantity and quality of light be furnished. — 

 That it may be perfectly free from color, an achromatic condenser is 

 employed, and that fine markings and minute shadings may be 

 brought out. The light is sometimes polarized : at other times it is 

 made to diverge from the object, as if it were self-luminous ; some- 

 times it must reflect the light ; at others transmit it ; each class of 

 objects requiring a difi'erent management in the illumination. 



In order that the views given by the instrument may be drawn, a 

 camera lucida is attached to the tube, by which the image is thrown 

 down on paper, and can thus be readily traced with pen or pencil ; 

 Sometimes a photographic apparatus is employed, by which the 

 magnified view is daguerreotyped in all its accuracy and beauty. 



A mechanical stage upon which the object is placed to be viewed, 

 is also a necessary adjunct. Suppose we are using a power of one 

 thousand, and wish to move the object about that we may view all 

 its parts ; if we take hold of it with the hand, we may if very care^ 

 ful and steady move it as little as the one tenth of an inch ; but this 

 small motion would be magnified by the power employed, and it 

 would consequently appear to move one hundred inches, or more 

 than eight feet ; passing out of view with the velocity of lightning. 

 To remedy this, the stage itself is made moveable in every direc- 

 tion by means of racks and pinions, or a lever. In the engraving, 

 two milled heads will be seen attached to the stage. By turning 

 these, the observer can move the object slowly or rapidly, in any 

 direction ; he can even follow bodies in motion, such as swimming 

 animalculfe, and keep them, despite their lively dancing, constantly 

 in the field of view. 



There are many other adjuncts such as reflecting prisms, mirrors, 



