THE COMPOUND MICROSCOPE 



must fix our second lens at this point for we now 

 have a compound microscope, a very crude one cer- 

 tainly and without the trimmings which make the 

 microscope so useful. Before we proceed to explain 

 what has happened to the light rays we must take 

 our paper screen once more and place it as near as 

 possible to the spot where our eye was situated when 

 we saw the second image. We shall find that, how- 

 ever much we may move our screen to or from the 

 second lens we can never manage to obtain an image 

 upon it for the reason that this second image is 

 virtual, but unlike the first image it is not inverted. 

 One or two diagrams will help to explain our 



experiment and, instead of the lighted candle, we 

 will suppose that our object is an arrow — it is easier 

 to draw and serves just as well. The magnification 

 of the object by our first lens may be represented 

 by the diagram below, where AA is the lens, CD 

 the object and D^ C^ its image. 



The arrow C^D^ shows the point at which we 

 placed our screen, and as our diagram shows, the 

 image is magnified and inverted. 



Our second lens, we remember, was focussed on 

 the back of the paper, placed at C^ D^ ; for practical 

 purposes we may ignore the thickness of the paper 

 and say that it was focussed on the image C^ D^. 

 Had we left it at that, the further course of the 



53 



