8 



SIMPLE AND COMPOUND MICROSCOPES 



[Ch. I 



§ 5. Virtual images. — In all diagrammatic drawings showing 

 the microscope when looking directly into it, an enlarged, imaginary 



Object 



Fig. 5-6. Vision by the Unaided Eye and by the Aid of a Simple 



Microscope. 



Fig. 5. Unaided Eye Vision. Axis, the Principal Optic Axis of the 



Eye Extended to the Object. 



Object The object to be seen; it is at a distance of 250 millimeters from the 

 eye. 



r i The retinal image; it is inverted. 



Fig. 6. Vision by the Aid of a Simple Microscope. Axis, Principal 

 Optic Axis of the Microscope and of the Eye. 



A 1 B 1 The object within the principal focus (F) of the lens. 



S M A double convex lens acting as a simple microscope. 



Cr The cornea of the eye. 



R Single refracting surface of the schematic eye. 



L The crystalline lens of the eye. 



B 2 A 2 The retinal image; it is inverted. 



A 3 B z The virtual image projected into the field of vision at 250 milli- 

 meters; it is erect, and the appearance is exactly as if the virtual image were 

 an object as in fig. 4, and no lens were present. 



object is shown out in space. This is frequently called a virtual image. 

 If there were no microscope and an object of that size were in front 

 of the observer, he would get the same appearance, for a retinal image 

 of the same size would be produced as is produced by the magnifying 



