Ch. I] 



SIMPLE MICROSCOPE EXPERIMENTS 



15 



of the object from that center. In a word, the nearer the object to 

 the focus, the farther away the image from that point, and the greater 

 the relative size of the image. This is equally true of real and of 

 virtual images (fig. 13-16). 



<<»ar 



Experiments with the Simple Microscope 



§ 14. For a simple microscope use a reading glass, or any form of 

 simple microscope such as the tripod magnifier (fig. 17, 18). Hold 

 the magnifier over a printed 

 page and look through the 

 magnifier. The letters and 

 words will appear as they do 

 with the naked eye, but larger 



(fig. 4). 



In order to get the sharpest 

 image it will be necessary to 

 raise and lower the magnifier 

 until the best position is 

 found. This mutual arrange- 

 ment of magnifier and object 

 is called focusing, or getting 

 into focus. 



§ 15. Size of the field. — 

 With any given magnifier, the 

 size of the field, that is the 

 area which can be seen, is 

 larger with the eye near the 

 magnifier. 



Demonstrate this by hold- 

 ing the eye 10 to 20 cm. above 

 the tripod magnifier and noting the number of letters or words which 

 can be seen. Then lower the head till the eye is only 2 to 5 cm. from 

 the magnifier, and again note the number of letters or words which 

 can be seen. It will be necessary to focus the magnifier for each 

 position of the eye. 



Fig. 15-16. Virtual Image with the 

 Object near to and far from the PRIN- 

 CIPAL FOCUS. 



/./,/,/ The principal foci on the axis 

 above and below the lens. 



Lc, Lc The same lens to show the dif- 

 ference in size of the virtual image with 

 the object near to and far from the princi- 

 pal focus. 



cp Tin- r\ e point. 



.1 B, .1' B' The object and its erect 

 virtual image. 



