138 



MAGNIFICATION OF THE MICROSCOPE 



[Ch. V 



Put the 8x or iox ocular in place of the 4.x or 5X, and then put the 

 camera lucida in position. Measure the size of the image with di- 

 viders and a rule as be- 

 fore. The power will be 

 considerably greater than 

 when the low ocular was 

 used. This is because the 

 virtual image (fig. 78) seen 

 with the high ocular is 

 larger than the one seen 

 with the low one. 



Lengthen the tube of 

 the microscope 50-60 mm. 

 by pulling out the draw- 

 tube. Remove the camera 

 lucida and focus; then re- 

 place the camera and ob- 

 tain the magnification. It 

 is greater than with the 

 shorter tube. This is be- 

 cause the real image (fig. 

 83) is formed farther from 

 the objective when the 

 tube is lengthened, and 

 the objective must be 

 brought nearer the object. 

 The law is : the magnifica- 

 tion varies directly with 

 the relative distance of the 

 image and object from the 

 center of the lens (fig. 84) ; 

 thus, if the image is four 

 times as far from the 

 center of the lens as the 



Objeslive 



Object-b 

 Object-a 



Fig. 83. To Show the Relative Position 

 of the Object and the Real Image. 



The farther from the lens the object, the 

 nearer to it will be the real image (Object-a, 

 Image-a; and Object-b, Image-b). 



axis The principal optic axis extended 

 above and below. 



Secondary axis a and b The secondary axes 

 at the limits of the respective images, and 

 objects. 



object, then it will be four times as large as the object, and if it is 

 one-fourth as far from the center of the lens as the object it will be 

 only one-fourth as big as the object, and so on. 



