CONTENTS. yii 



PAGE 



60. Effects of atmospheric electricity on the wires. 61. 

 Lightning conductors. 62. Those of Messrs. Walker and 

 Breguet. 63. Conducting current into stations. 64. Under- 

 ground wires. 65. Methods of insulating them. 66. Testing 

 posts . 129 



CHAP. III. 67. Wires of Magneto- electric Telegraph Company. 

 68. Mr. Bright' s method of detecting faulty points. 69. Such 

 failure of insulation rare. 70. Underground method recently 

 abandoned in Prussia. 71. Underground wires of the European 

 and Submarine Company. 72. Imperfect insulation in tunnels. 

 73. Mr. Walker's method of remedying this. 74. Overground 

 system adopted through the streets of cities in France, and in 

 the United States. 75. Telegraphic lines need not follow rail- 

 ways. 76. Do not in America. 77. Submarine cables. 78. 

 Cable connecting Dover and Calais. 79. Failure of first attempt 

 Improved structure. 80. Table of submarine cables and their 

 dimensions. 81. Dimensions and structure of the Dover and 

 Calais cable. 82. Holyhead and Howth cable. 83. First at- 

 tempt to lay cable between Portpatrick and Donaghadee its 

 failure. 84. Dover and Ostend. 85. Portpatrick and Donagha- 

 dee. 86. Orfordness and the Hague 145 



CHAP. IV. 87. Cable between Spezzia and Corsica. 88. Other 

 cables, European and American. 89. Objections brought by 

 scientific authorities to the submarine cables. Answers to these 

 by practical men. 90. Example of a cable uninjured by the 

 action of the sea. 91. Precautions necessary in laying the cable. 

 92. Accident in laying the Calais cable. 93. Imperfection 

 attributed to the Belgian cable. 94. Transatlantic Ocean Tele- 

 graph. 95. Underground wires between the Strand and Loth- 

 bury. 96. Effect of the inductive action of underground or 

 submarine wires. 97. Possible influence of this on telegraphic 

 operations. 98. Examples of overground wires extended to great 

 distances without intermediate support between Turin and 

 Genoa. 99. Telegraphic lines in India. 100. Difficulties arising 

 from atmospheric electricity height and distance of posts mode 

 of laying underground wires extent of line erected to April 

 1854. 101. Intensity of current decreases as the length of wire 



increases. 102. Also increases with the thickness of the wire. 



103. And with the number of elements in the battery. 104. 



Result of Pouillet's experiments on the intensity of current. 

 105. Intensity produced by increasing the power of the battery. 

 : 106. How the current produces telegraphic signals. 107. 

 Velocity of the current. 108. Transmission of signals instan- 

 taneous lg^ 



CHAP. V. 109. Current controlled by making and breaking the contact 



of conductors. 110. Instruments for controlling the current. 



Commutators. 111. General principle of the commutators. 



112. Its application to telegraphic operations. 113. To trans- 

 mit a current on the up-line only. 114. On the down-line only. 

 115. On both lines. 116. To reverse the current. 117. To 

 suspend and transmit it alternately. 118. How to manage a 



