20 



THE MICROSCOPE. 



foci, forms an image, which the second 

 lens treats as an original object, and mag- 

 nifies it just as the single microscope mag- 

 nified the object itself. 



The annexed figure (12) shows the 

 course of the rays through a compound 

 microscope of two lenses. The rays pro- 

 ceeding from the object A B are so acted 

 upon by the lens C D, near it, and thence 

 called the object glass, that they are con- 

 verged to foci in A' B', where they form 

 an enlarged image of the object, as would 

 be evident if a piece of oiled paper or 

 ground glass were placed there to receive 

 them. They are not so intercepted, and 

 therefore the image is not rendered visi- 

 ble at that place; but their further pro- 

 gress is similar to what it would have been 

 had they really proceeded from an object 

 at A' B'. They are at length received by 

 the eye-lens L M, which acts upon them 

 as the simple microscope has been de- 

 scribed to act on the light proceeding 

 from its objects. They are bent so that 

 they may enter the eye at E in parallel 

 lines, or as nearly so as is requisite for 

 distinct vision. When we say that the 

 rays enter the eye in nearly parallel lines, 

 we mean only those which proceed from 

 one point of the original object. Thus 

 the two parallel rays M E have proceeded 

 from and are part of the cone of rays 

 CAD, emanating from the point A of 

 the arrow; but they do not form two pic- 

 tures in the eye, because any number of 

 parallel rays which the pupil can receive 

 will be converged to a point by the eye, 

 and will convey the impression- of one 

 point to the mind. In like manner the 



