96 A HALF-HOUR WITH 



CHAPTER VII. 

 A HALF-HOUK WITH POLARIZED LIGHT. 



WHAT is polarized light, and in what does it 

 differ from ordinary light ? This question is often 

 asked, and, like many other questions in physical 

 and natural science, more easily asked than an- 

 swered. 



To enable the young microscopist to form some 

 conception of the difference between common or 

 ordinary light and that known as polarized light, 

 it will be necessary to form some definite idea of 

 light itself. 



Light, according to the modern theory, is pro- 

 duced by the vibrations or undulations of an ima- 

 ginary fluid called ether ; this is supposed to be a 

 rare and highly elastic fluid, occupying all space 

 and pervading all bodies : the vibrations of this 

 medium produce light, just as the vibrations of 

 air produce sound. 



The length of these vibrations is inconceivably 

 minute, and their rapidity is represented by num- 

 bers which the human mind can scarcely compre- 

 hend. Upon the relative lengths of these vibra- 

 tions depend the differences of colour, red being 

 produced by the longest, and violet by the shortest 

 waves or vibrations. 



For the production of the red ray, 37,640, and 

 for the violet ray 59,750 undulations in an inch 

 are requisite. In the production of the red ray 

 458 millions of millions, and in the violet ray 

 727 millions of millions of undulations take place 



