CONTENTS. xv 



CHAPTER X. 



COMBINED ENGINES, HOT-AIR, AND GAS-ENGINES. 



PAGB 



I. Combined Engines 503 



II. Hot- Air Engines 506 



III. Gas-engines ' 509 



BOOK V. 

 MAGNETISM AND ELECTRICITY. 



CHAPTER I. 



THE COMPASS. 



I. The Declination Compass Its Uses 519 



II. Dip Circles. Terrestrial Magnetism 527 



CHAPTER II. 



LIGHTNING-CONDUCTORS. 



I. The Principles on which Lightning-conductors are Constructed . . 531 

 II. Description and Arrangement of Lightning-conductors 536 



CHAPTER III. 



ELECTRIC TELEGRAPHY. 



I. Invention of Electric Telegraphy 543 



II. The Electric Telegraph General Theory 546 



III. Needle Telegraphs . . . |S&j 548 



IV. Dial Telegraphs ' . 559 



V. Dial Telegraphs (continued] 567 



VI. Wheatstone's Magneto- Alphabetical Telegraph 573 



