36 



MICROSCOPE AND ACCESSORIES 



[CH. I 



this image being formed on the opposite side of the objective from 

 the object (Fig. 26). 



FUNCTION OF AN OCULAR 



§ 64. Using the same objective as for § 53, get as clear an 

 image of the letters as possible on the lens paper or ground-glass 

 screen. Look at the image with a simple microscope (Fig. 19, 21) 

 as if the image were an object. 



Observe that the image seen through the simple microscope is 

 merely an enlargement of the one on the screen, and that the letters 

 remain inverted, that is they appear as with the naked eye (§ 12). 

 Remove the screen and observe the aerial image with the tripod. 



Put a 50mm. (A, No. 1 or 2 in.), ocular i. e., an ocular of 

 low magnification in position (§ 55). Hold the eye about 10 to 

 20 millimeters from the eye-lens and look into the microscope. The 

 letters will appear as when the simple microscope was used (see 



Fig. 43. Diagram, of the simple microscope 

 showing the course of the rays and all the images, 

 and that the eye forms an integral part of it. 



A x B 1 . The object within the principal focus. 

 A* Z?3. The virtual image on the same side of 

 the lens as the object. It is indicated by dotted 

 lines, as it has no actual existence. 



2? 2 A". Retinal image of the object (A' B 1 ) 

 The virtual image is simply a projection of the 

 retinal image into the field of vision. 



Axis. The principal optic axis of the micro- 

 scope and of the eye. Cr. Cornea of the eye. L. 

 Crystalline tens of the eye. R. Ideal refracting 

 surface at which all the refractions of the eye may 

 be assumed to take place. 



above), the image will become more distinct by slightly raising the 

 tube of the microscope with the coarse adjustment. 



§ 65. The Function of the Ocular, as seen from the above, 

 is that of a simple microscope, viz. : It magnifies the real image 

 formed by the objective as if that image were an object. Compare 

 the image formed by the ocular (Fig. 26), and that formed by a. 

 simple microscope (Fig. 43). 



