STRUCTURE OF A LENS. 



15 



to the discovery of what is popularly termed its 

 magnifying power, but in reference to which many 

 errors prevail. The following diagrams will aid 

 the reader. 



MN is an object placed before a convex lens L L, 

 every point of which will send forth rays in every 

 direction. Those rays which fall upon the lens will 

 be refracted to foci behind the lens. Since the focus 

 where any point of the object is represented in its 

 image is in the straight line drawn from that point 

 of the object through the middle point c of the lens, 

 the upper end M of the object will be represented 

 somewhere in the line M c m, and the lower end N 

 somewhere in the line N c n, that is, at the points m, n, 

 where the rays L m, L m, L n, L n, cross the lines 

 M c m, N c n. Hence m will represent the upper, 

 and n the lower end of the object m n. It is also 

 evident, that in the two triangles M c N, m c n, m n, 

 the length of the image, must be to M N, the length 

 of the object, as c m, the distance of the image, is to 

 c M, the distance of the object from the lens. 



