x CONTENTS 



CHAPTER IV 



PAGE 



MACHINES . '; . . . . . . :.. . . 53 



The Evolution of Machines. The Principle of Work. 

 The Lever. Classes of Levers. Pulleys. Wheel and 

 Axle. The Inclined Plane. The Screw. The Wedge. 

 Mechanical Advantage. Efficiency in Machines. Power. 



Unit of Power. Water Power. The Overshot Wheel. 



The Undershot Wheel. The Water Turbine. Wind 

 Power. The Aeroplane. The Steam Engine. The 

 Steam Turbine. Gasoline Engines. 



CHAPTER V 



THE ATMOSPHERE , . . .' . . , . . 73 



Weight of the Atmosphere. Air Pressure. Changes 

 in Atmospheric Pressure Due to Elevation. The Common 

 Pump. The Force Pump. The Centrifugal Pump. 

 The Siphon. Compressed Air. Oxygen. Oxygen and 

 Ljfe. Nitrogen. Air, a Mixture. Respiration. The 

 Lungs. The Air Passages. Mechanism of Breathing. 

 Mouth Breathing. Adenoids. Colds. 



CHAPTER VI 



WATER - . . . . , . . . ... 93 



Electrolysis of Water. Water by Synthesis. Physical 

 and Chemical Changes. Preparation of Hydrogen. 

 Properties of Hydrogen. Three States of Water. 

 Freezing of Water. Steam. Solutions. Properties of 

 Solutions. Water of Crystallization. Evaporation. 

 Evaporation, a Cooling Process. 



CHAPTER VII 



USES OF WATER . ' . 108 



Manufacture of Ice. Cold Storage. Occurrence of 

 Water in Nature. Water Pressure. Water Pressure on 

 the Sides of a Tank. - - Transmission of Pressure by 

 Liquids. The Hydraulic Press. Artesian Wells. 

 Archimedes' Principle. Submarines. Density of a Solid 



