i8 



BACTERIOLOGY 



image. Our subjective interpretation of the stimulation of the 

 retina (i.e., what we see) is influenced by other psychological 

 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 



\h 



r 



Fig. 4. — Image formation by two'^Ienses in series, with magnification of two 

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

 angle. 



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 

 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 



Fig. S- — 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. 



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

 so as to focus upon the same screen slightly divergent rays pro- 

 ceeding from the object. It will further be perceived that the 

 sine of the angle of divergence of the beam proceeding from the 

 object varies directly with the magnification achieved, and further 



