CH. /] 



MICROSCOPE AND ACCESSORIES 



dent should study the figure with a microscope before him and become thoroughly 

 familiar with the names of all the parts. See also the cuts of microscopes at the 

 end of Ch. II. 



OPTICAL PARTS 



\ 14. Microscopic Objective. This 

 consists of a converging lens or of one 

 or more converging lens-systems, which 

 give an enlarged, inverted, real image of 

 the object ( Figs. 14, 21 ). And as for the 

 formation of real images in all cases, 

 the object must be placed outside the 

 principal focus, instead of within it, as 

 for the simple microscope. (See | n, 

 53, Figs. 1 6, 21.) 



Modern microscopic objectives usu- 

 ally consist of two or more systems or 

 combinations of lenses, the one next 

 the object being called the front com- 

 bination or lens, the one farthest from 

 the object and nearest the ocular, the 

 back combination or system. There may 

 be also one or more intermediate sys- 

 tems. Each combination is, in general, 

 composed of a convex and a concave 

 lens. The combined action of the sys- 

 tem serves to produce an image free 

 from color and from spherical distor- 

 tion. In the ordinary achromatic ob- J 

 jectives the convex lenses are of crown 

 and the concave lenses of flint glass 

 (Figs. 22,23). . 



FIG. 21. Diagram showing the 

 principle of a compound microscope with 

 the course of the rays from the object 

 (A B) through the objective to the real 

 image (B' A'}, thence through the ocu- 

 lar and into the eye to the retinal image 

 (A*B 2 ), and the projection of the retinal 

 image into the field of vision as the 

 virtual image (B^A*). 



AB. The object. A*B\ The retinal 

 image of the inverted real image, (B l A l ) , 

 formed by the objective. B^A*. The 

 inverted virtual image, a projection of 

 the retinal image. 



c 



