784 Botanical Microtechnique 



the receptive surface on which the image is formed. If an object is 

 held at a given distance in front of the e)e an inverted image of 

 definite size is produced on the retina. If a larger object is substittited 

 at the same distance, or if the original object is moved closer to the 

 eye, the visual angle, or the angle of the cone of rays between the 

 object and the eye, is increased, the size of the retinal image is in- 

 creased, and the object appears to be larger. In Fig. 16.2 A compare 

 the two objects shown in solid and dotted lines, respectively, their 

 respective visual angles Va^, Va.,, and the retinal images Ri^, Ri.2- 



When the eye is held at the eyepoint of the microscope, it inter- 

 cepts the image-forming cone which has a definite angle established 

 by the microscope, and a retinal image of definite size is produced 

 (Fig. 16.2 5). The observer sees a magnified virtual image, which 

 appears to be near the level of the microscope stage, approximately 

 10 in. from the eye. The retinal image is erect, the virtual image is 



Object, 



Objectj 



r--. 



J a 



Object Objective 



Primary 

 image 



Ocular 



Reilnal 

 image 



B 



Virtual image 



Fk;. 16.2— a. Formation of imai^cs hv the eye showinj; relative size of retinal image 

 in relation to \isnal anj;ic: />'. leiiiial and \irtual imai^es ol)taine(i with a (omponnd 



luinoscopc. 



