CIL xxxin. INTERFERENCE OF LIGHT. 3*5 





CHAPTER XXXIII. 



SCIENCE OF THE NINETEENTH CENTURY (CONTINUED). 



Dr. Young explains the Interference of Light Malus discovers the 

 Polarization of Light caused by Reflection Fresnel Polarization 

 of Light explained by Young and Fresnel Sir David Brewster and 

 M. Biot on colours produced by Polarization Fizeau Foucauk 

 Velocity of Light Colour Theory of Young and Helmholtz. 



WE must now go back to the history of Light, which we 

 left, as you will remember, at the end of the seventeenth 

 century, at the point which Newton and Huyghens had 

 readied. During the whole of the eighteenth century very 

 little was learnt about this science, and it remained for the 

 men of our own time to make the next step and to discover 

 the grand laws of light which we must now consider. It 

 will be best to divide our subject into two parts ist. The 

 discoveries which have led to a true Theory of Light. These 

 are very difficult to understand, and you must not expect 

 to gain more than a slight notion of them ; 2d. The new 

 facts lately discovered about* the Chemistry of Light, and 

 called Spectrum Analysis, and of these I hope you may 

 understand enough to fill you with delight at the beautiful 

 histories they reveal. 



Discovery of the Interference of Light by Young, 

 1801. You will remember that Newton and Huyghens had 

 proposed two different theories of light (see page 174) 



