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BACTERIOLOGY 



retina distance divided by the object-lens distance. The longer 

 the antero-posterior diameter of the eye, the larger will be the 

 retinal image. Our subjective interpretation of the stimulation 

 of the retina (i.e., what we see) is influenced by other psycholog- 



FIG. 4. Image formation by two lenses in series, with magnification of two 

 diameters. Note that the opening angle of the beam is twice as large as the closing 

 angle. 



ical elements and especially by the memory of things seen before. 

 When two lenses are disposed in series so that the rays of 

 light coming from a point in the object pass through both lenses 

 before coming to a focus, we find the possibilities shown in Figs. 3, 

 4 and 5. In the figures it will be seen that the image produced 



FIG. 5. Image formation by two lenses in series, with magnification of three 

 diameters. Note that the opening angle of the beam is three times as large as the 

 closing angle. 



when the first lens is in position so as to render the rays parallel 

 (Fig. 4), is just five times as large as that produced when it is 

 left out (Fig. 2), assuming that the second lens is capable of 

 change so as to focus upon the same screen slightly divergent 



