CONTENTS. 



SECTION II. 



Page 



Cohesion 42 



Strength of Materials 43 



Capillary Attraction 47 



Ascent of Sap 49 



SECTION III. 



Centre of Gravity 50 



Line of Direction 52 



CHAPTER IV. 



SIMPLE MACHINES, OR MECHANICAL POWEES. 

 SECTION I. 



Advantages of Machines 60 



Law^ of Virtual Velocities 61 



SECTION II. 



The Lever 63 



SECTION III. 



Estimating the Power of Levers 67 



Combination of Levers 70 



Weighing Machine 71 



Machines for extracting Stumps 72 



SECTION IV. 



Wheel and Axle 75 



Mole-plow 78 



Band and Cog Wheels 79 



Form of Teeth or Cogs 80 



SECTION V. 



The Pulley 83 



SECTION VI. 



The Inchned Plane 86 



Ascent in Roads 87 



Form and Materials for Roads 90 



Importance of good Road.s 92 



SECTION VII. 



The Wedge 93 



The Screw 94 



