THE M1CEOSCOPE. 



of the light's rays in their passage to the eye, in 

 such manner as to bring the image formed by the 

 object-glass into a condition to be seen by the eye- 

 glass. A stop also is placed between the two lenses 

 in such a position that all the outer rays, which pro- 

 duce the greatest amount of distortion, arising from 

 spherical and chromatic aberration, are cut off. The 

 short tube carrying the lenses (fig. 2) slides freely, 

 but without looseness, into the upper end of the com- 

 pound body, A, an arrangement which affords a ready 

 and convenient method for changing the eye-pieoe. 



Compound Microscopes 

 are generally fitted up 

 with two eye-pieces, the 

 one deep and the other 

 shallow. The last has its 

 lenses close together, and 

 magnifies the most, whilst 

 the other has them far- 

 ther apart, and magnifies 

 less. In the use of these 

 eye-pieces, it should never 

 be forgotten that the one 

 which magnifies least is 

 generally the most trust- 

 worthy. 



At the opposite end of the tube A is the object- 

 glass C. The use of this lens is to collect and 

 bring to a point the rays of light that proceed 

 from any object placed in its focus. At this point 

 an enlarged image of the object will be formed in 

 the focus of the eye-glass. We have only to look 

 through the latter at the picture thus formed in 

 order to obtain a second image larger than the 

 first. And this is the way in which minute objects 

 are made to appear so much larger than when seen 

 by the unassisted eye. It will at once be seen how 



Fig. 2. Eye-piece. 



