



CHAPTER III 



THE ACTION OF LIGHT 



IT is hardly necessary to remark that the 

 wonderful properties of the microscope de- 

 pend upon light. Without light, lenses would 

 be useless, objects could not be illuminated and 

 we oculd not see them. In this short chapter 

 we propose to give a brief outline of the action 

 of light; if our words appear to savour of the 

 school-book, we shall try to avoid it, but, we 

 repeat, if they do so we would remind our readers 

 that the more one knows of the action of light the 

 better use one can make of one's instrument. As 

 a well-known microscopist has remarked we may be 

 able to afford a costly harp or a costly microscope, 

 but although we may be able to strike a few notes 

 on the former and examine a few objects with the 

 latter, we can only make the best use of either by 

 thoroughly understanding and practising upon it. 



The first thing we learn when we study light is 

 that it travels in straight lines. The chief source of 

 light to the inhabitants of this earth is the sun. 

 Now the sun is so far away that, for all practical 

 purposes, the rays of light coming from it may be 

 looked upon as being parallel to one another. That 



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