First use of sails for propelling boats, p. 62--The fire engine of Ctesibius, p. 63--Suction and pressure as studied by the ancients, p. 64--Studies of air pressure, p. 65--The striking demonstration of Von Guericke, p. 66--The sailing chariot of Servinus, 1600 A.D., p. 68--The development of the windmill, p. 69--The development of the water-wheel, p. 70--The invention of the turbine, p. 72--Different types of turbines, p. 73--Hydraulic power and its uses, p. 74--The hydraulic elevator, p. 76--Recent water motors, p. 77. CHAPTER V CAPTIVE MOLECULES: THE STORY OF THE STEAM ENGINE The development of the steam engine, p. 79--The manner in which energy is generated by steam, p. 80--Action of cylinder and piston, p. 81--Early attempts to utilize steam, p. 82--Beginnings of modern discovery, p. 83--The "engine" of the Marquis of Worcester, p. 84--Thomas Savery's steam pump, p. 85--Denis Papin invents the piston engine, p. 88--Newcomen's improved engine, p. 89--The use of these engines in collieries, p. 90--The wastefulness of such engines, p. 92--The coming of James Watt, p. 93--Early experiments of Watt, p. 95--The final success of Watt's experiments, p. 97--Some of his early engines, p. 98--Rotary motion, p. 99--Watt's engine, "Old Bess," p. 101--Final improvements and missed opportunities, p. 102--The personality of James Watt, p. 107. CHAPTER VI THE MASTER WORKER Improvements on Watt's engines, p. 110--Engines dispensing with the walking beam, p. 111--The development of high-pressure engines, p. 112--Advantages of the high-pressure engine, p. 114--How steam acts in the high-pressure engine, p. 116--Compound engines, p. 117--Rotary engines, p. 119--Turbine engines, p. 124--The _Turbinia_ and other turbine boats, p. 125--The action of steam in the turbine engine, p. 126--Advantages of the turbine engine, p. 127. CHAPTER VII GAS AND OIL ENGINES Some early gas engines, p. 133--Dr. Stirling's hot-air engine, p. 133--Ericsson's hot-air engines, p. 134--The first practical gas engine, p. 135--The Otto gas engine, p. 136--Otto's improvement by means of compressed gas, p. 138--The "Otto cycle," p. 139--Adaptation of gas engines to automobiles, p. 140--Rapid increase in the use of gas engines, p. 141--Defects of the older hot-air engines, p. 145--Recent improvements and possibilities in the use of hot-air engines, p. 146. CHAPTER VIII THE SMALLEST WORKERS The relative size of atoms and electrons, p. 148--What is electricity? p. 149--Franklin's one-fluid theory, p. 150--Modern views, p. 153--Cathode rays and the X-ray, p. 156--How electricity is developed, p. 159--The work of the dynamical current, p. 162--Theories of electrical action, p. 165--Practical uses of electricity, p. 168. CHAPTER IX MAN'S NEWEST CO-LABORER: THE DYNAMO