CONSTRUCTION OF THE MICROSCOPE. 



29 



and down by means of two small handles projecting from the cell in 

 which the lens is set. Two small tubes i, with either a condensing 

 lens for opaque objects, or a pair of forceps, may be attached to this 

 side of the stage. The magnifiers are either simple lenses or doublets; 

 or it could be easily converted into a compound microscope by insert- 

 ing a compound body, supported on a bent arm, in the place of the one 

 carrying the single lenses. 



THE COMPOUND MICROSCOPE. 



The compound microscope may, as before stated, consist of only two 

 lenses, while a simple microscope has been shown 

 to contain sometimes three. In the triplet for 

 the simple microscope, however, it was explained 

 that the object of the first two lenses was to do 

 what might have been accomplished, though not 

 so well, by one ; and the third merely effected 

 certain modifications in the light before it entered 

 the eye. But in the compound microscope the 

 two lenses have totally different functions : the 

 first receives the rays from the object, and bring- 

 ing them to new foci, forms an image, which the 

 second lens treats as an original object, and mag- 

 nifies it just as the single microscope magnified 

 the object itself. 



Fig. 25 shows the earliest form of the com- 

 pound microscope, with the magnified image of a 

 fly, as given by Adams, which he describes as con- 

 sisting of an object-glass, In, and an eye-glass, /gr ; 

 the object, b' o, being placed a little further from 

 the lens than its principal focal distance, the pencil 

 of rays from which converge to a focus, and form 

 an inverted image of the object at p q, which 

 image is viewed by the eye placed at a through 

 the eye-glass ygr. The rays remain parallel after 

 passing out until they reach the eye, when they 

 will converge by the refractive powers of this 

 organ, and be collected on the retina. But the — 



image differs from the real object in a very essen- fig, 25. 



tial particular. The light being emitted from the 

 object in every direction, renders it visible to an eye placed in any 



