CHAPTER 1 



Principles of Microscopy 



The word microscope means "little seer" or "seer of little things." The 

 first simple microscopes were glass globes filled with water, and Pliny 

 has left a record of their use in the first century. No one, however, can 

 examine the carved gem stones of antiquity without realizing that micro- 

 scopes were in use at least five hundred years earlier. There is no theo- 

 retical limit to the magnifying power of such simple lenses, and Loewen- 

 hoek was able to make them so well that he discovered bacteria. He 

 never saw what we now call a microscope. 



LENSES AND IMAGES 



There are many practical disadvantages to simple lenses of high mag- 

 nifying power. The distortions they produce, which will be discussed 

 later, are not the chief of these. The greatest objection is that focal 

 length decreases as magnifying power increases so that Leeuwenhoek had 

 almost to push his eye into his lenses to see anything. This difficulty was 

 overcome, about the year 1600, by using the newly invented telescope 

 to examine from a reasonable distance the image made by a simple lens. 

 This is exactly what we do today when we use what is now called a mi- 

 croscope, shown diagrammatically in Fig. 1. 



OBJECTIVE 







OBJECT 



OCULAR 



> 



li 

 IMAGE OF 



IMAGE OF h IMAGE OF |2 



IMAGE OF 1 3 



Fig. 1. Diagram to show production of image by a compound microscope. A mag- 

 nified image at l\, thrown by the objective, is examined through a telescopic device 

 known as the ocular, from which an image is formed on the retina by the lens of 

 the eye. 



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