10 



VIEWS OF THE MICROSCOPIC WORLD. 



verge accurately on the other side of the lens to points corresponding to those 

 whence they proceeded, and thus form an image. This is seen by a glance at 

 Figure 2. Figure 2, where E D represents a 



lens, R L its focal distance, ABC 

 an object placed a little farther from 

 the lens than its focal distance, and 

 F G H an image of the object on the 

 opposite side of the lens. From the 

 point of the arrow at C the rays 

 C E, C L, and C D, proceed, which 

 are refracted to the same point at F, 

 and there combine to form an image 

 of the point. 



What is true of the rays emanat- 

 ing from the point C, is likewise true 

 of those proceeding from every point on the surface of the object directed 

 towards the lens : each converge on the opposite side of the lens to correspond- 

 ing points in the image. The linear magnifying power of the object-glass is esti- 

 mated according to the following rule, that the length or breadth of the object 

 bears the same relation to the length or breadth of the image, as the distance of 

 the object from the centre of the lens does to the distance of the image from the 

 centre. Thus, if the object is six inches from the centre and the image six feet, 

 it is magnified in length and breadth twelve times, and the surface of the object 

 is magnified twelve into twelve, or one hundred and forty-four times. 



Figure 3. To illustrate from the figure ; the length 



and breadth of the image F H, exceeds 

 the length and breadth of the object, as 

 many times as the line B L is contained 

 in the line G L. The mode in which an 

 object is magnified by the Compound 

 Microscope is shown in Figure 3, where 

 A B represents 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 G H. By this lens the divergent 

 rays of light proceeding from the image 

 F E, have their direction so changed, that 

 entering the eye 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 magnifying 

 power of the instrument is equal to the combined effect of the two glasses, and is 

 estimated as follows : The image F E, is as much larger than the object A B, as 

 its distance from the centre of the object-glass C D, exceeds the distance of A B 

 from the same point ; and the image K L, is as many times greater than F E, as 



