THE COMPOUND MICROSCOPE 



one capable of magnifying more than the other, a 

 sheet of paper and a candle. We must darken the 

 room in which we make the experiment and, having 

 lighted the candle, we may proceed to make a com- 

 pound microscope, for that is really what we are 

 about to do. Taking the lens which gives the 

 greatest magnification, we look through it till we 

 can see a clearly defined image of the lighted candle, 

 then we fix the lens at that spot, so that, during 

 the rest of our experiment, the candle and lens 

 remain at the same distance from one another. Now 

 we put the piece of paper as nearly as we can in the 

 position of our eye, moving it nearer or further from 

 the lens till we have a perfectly clear image of the 

 candle thrown upon it. The first thing to strike us 

 is that the image is upside down; it is known as 

 a real, inverted image. Real because it can be 

 thrown upon a screen and inverted — well because it 

 is upside down. There are some images, as we shall 

 learn in a moment, which can be seen but which 

 cannot be thrown upon a screen : they are called 

 virtual images. 



Having fixed our sheet of paper in position, we 

 take our second lens, focus it sharply upon the back 

 of the sheet of paper, being careful to keep the 

 centres of the two lenses as far as possible in a 

 straight line with one another. Having obtained 

 a sharp image we remove the paper and gradually 

 advance our second lens towards the first. We soon 

 reach a point where we have a very much larger 

 image of the candle than the first lens gave us ; we 



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