CONTENTS. 
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Introduction ..1 to 3 
The three main problems of the telegraph, 1—The agents employed 
in telegraphy, 2—Electricity the most effective agent, 3. 
PART I. 
OPTICAL TELEGRAPHY—ACOUSTIC TELEGRAPHY—PNEUMATIC 
TELEGRAPHY. 
CHAPTER I. 
Optical Telegraphy . . . . . . 4 to 23 
System of the Ancients, 4—Various methods before Chappe’s telegraph, 
5—Visual telegraph of Chappe and his brothers, 7—Chappe’s tele¬ 
graph adopted in 1793 by France, 9—Visual telegraphy used in the 
Crimean War, and subsequently, 12—Mangin’s optical telegraph for 
military purposes, 13—Leseurre’s heliographic apparatus, 17— 
Mance’s heliograph, 21—Thompson’s system of distinguishing 
lighthouses, 22. 
CHAPTER II. 
Acoustic Telegraphy .24 to 49 
Ancient systems, 24—Speaking tubes, 25—String telegraph, 26—Tele¬ 
phones, 28—Telephone companies, 31—Gower’s telephone, 32— 
Telephone exchanges, 35—The apparatus and mode of working, 39. 
CHAPTER III. 
Pneumatic Telegraphy .50 to 77 
History, 50—Arrangement of the tubes in London, 51—Carriers, 53— 
Varley’s valves, 54—Apparatus and engines for condensing and 
