Xll i CONTENTS. 



SECTION XV. 



Analysis of the Atmosphere Its Pressure Law of Decrease in Density Law 

 of Decrease in Temperature Measurement of Heights by the Barometer 

 Extent of the Atmosphere Barometrical Variations Oscillations Trade- 

 WindsMonsoons Rotation of Winds Laws of Hurricanes . Page 131 



SECTION XVI. 



Sound Propagation of Sound Illustrated by a Field of Standing Corn 

 Nature of Waves Propagation of Sound through the Atmosphere- 

 Intensity Noises A Musical Sound Quality Pitch Extent of Human 

 Hearing Velocity of Sound in Air, Water, and Solids Causes of the 

 Obstruction of Sound Law of its Intensity Reflection of Sound Echoes 

 Thunder Refraction of Sound Interference of Sounds . . 143 



SECTION XVII. 



Vibration of Musical Strings Harmonic Sounds Nodes Vibration of Air in 

 Wind-InstrumentsVibration of Solids Vibrating Plates Bells Har- 

 mony Sounding Boards Forced Vibrations Resonance Speaking Ma- 

 chines . 156 



SECTION XVIII. 



Refraction Astronomical Refraction and its Laws Formation of Tables of 

 Refraction Terrestrial Refraction Its Quantity Instances of Extraor- 

 dinary Refraction Reflection Instances of Extraordinary Reflection- 

 Loss of Light by the Absorbing Power of the Atmosphere Apparent 

 Magnitude.of Sun and Moon in the Horizon 171 



SECTION XIX. 



Constitution of Light according to Sir Isaac Newton Absorption of Light 

 Colours of Bodies Constitution of Light according to Sir David Brewster 

 New Colours Fraunhoffer's Dark Lines Dispersion of Light The 

 Achromatic Telescope Homogeneous Light Accidental and Complemen- 

 tary Colours M. Plateau's Experiments and Theory of Accidental 'Co- 

 lours 178 



SECTION XX. 



Interference of Light Undulatory Theory of Light Propagation of Light- 

 Newton's Rings Measurement of the Length of the Waves of Light, and 

 of the Frequency of the Vibrations of Ether for each Colour Newton's 

 Scale of Colours Diffraction of Light Sir John Herschel's Theory of the 

 Absorption of Light Refraction and Reflection of Light . . . 187 



