VIEWS OF THE MICROSCOPIC WORLD. 



INTRODUCTORY CHAPTER. 



THE MICROSCOPE, AND THE MOUNTING OF MICROSCOPIC OBJECTS. 



MICROSCOPES are divided into two classes, single and compound. The single mi- 

 croscope in its simplest form is a convex lens, and the magnified image of the object 

 passes at once to the eye of the observer ; the 

 object being magnified in the ratio of the focal 

 distance of the lens to the limit of distinct 

 vision, which varies from 5 to 10 inches in dif- 

 ferent persons. A single microscope is repre- 

 sented by Fig. 1, where A B is the lens; C D 

 an object placed in the principal focus of the 

 lens, at the distance H I ; and E F the magni- 

 fied image, seen at the distance of distinct vision 

 by the eye at N. The image exceeds the ob- 

 ject in length and breadth as much as N K is 

 larger than H I. 



The compound microscope must have at least 

 two lenses, viz., the object-glass and the eye-glass. 

 The office of the former is to produce a magrii- Fi &- * 



fied image of the object, which image is again magnified by the eye-glass, as if it was 

 an object: the eye-glass being, in fact, a single microscope. The compound micro- 

 scope is represented in Fig. 2, where A B is the object, D C the object-glass, 

 and F E the image of the object formed by the object-glass, so situated as to be 

 in the principal focus of the eye-glass 

 (T H. By this lens the divergent rays 

 of light proceeding from the image F E, 

 have their directions so changed, that 

 entering the e\ r e on the side of the lens 

 G- P H, a second magnified image is 

 clearly discerned at K L, at the limit 

 of distinct vision. The entire mag- 

 nifying power of the instrument is 

 e-\ual to the combined effect of the two 

 i^la^es, and is estimated as follows: 

 The imnge F E is as much larger than 

 the object A B, as its distance from 

 the centre of the object-glass C D ex- 

 ceeds the distance of A B from the same Fig. 8. 



