96 ANNUAL OF SCIENTIFIC DISCOVERY. 



America were probably equal in electrical power to 2000 battery cells, 

 while now it is found inexpedient to use more than two or three cells 

 in working the longest submarine lines in existence. Some of this 

 great power was no doubt used in the vain hope of forcing signals 

 through the line at a greater speed than the very slow and uuremuner- 

 ative rate at which it has alone been found possible to communicate 

 through an unbroken length of 3000 miles. The result was disastrous, 

 but the experience, though dearly bought, has proved of great value. 

 It has taught electricians the value of moderating the power used in 

 working lines, and above all has pointed out the imperative necessity 

 of having no single section of a submarine line of more than six hun- 

 dred miles in length. To lay long submarine cables in a continuous 

 length without intermediate stations has been found to answer no oth- 

 er purpose than that of greatly diminishing the speed of working and 

 multiplying every imaginable risk both of manufacture and submersion. 

 The Indian Government, acting under the judicious counsel of their 

 scientific advisers, have wisely determined to divide the Persian Gulf 

 cable into three sections, though its total length will not exceed 1500 

 statute miles." 



The Red Sea line was destroyed by faults of another character. 

 Being laid without any allowance for slack, that the cable might con- 

 form the more readily to the irregularities of the bottom, the suspended 

 portions became loaded with barnacles and coral, and crumbled from 

 its own weight. 



" To obviate this cause of danger, which in the above-mentioned 

 lines has probably occasioned a loss of property to the value of over a 

 million sterling, the Persian Gulf line is cased in twelve No. 7 gauge 

 harddrawn iron wires, thickly galvanized, so as effectually to prevent 

 their corrosion. But, in order to secure more effectually the perma- 

 nent stability of the line, the whole finished cable is thickly coated with 

 two servings of tarred hemp yarn, overlaid with two coatings of a 

 patent composition invented by Sir Charles Bright and Mr. Latimer 

 Clark. The composition consists of mineral pitch or asphalt, Stockholm 

 tar, and powdered silica, mixed in certain proportions, and laid on in 

 a melted state. While yet warm, it is passed between circular rollers, 

 which give it a round, smooth surface. When quite cold this forms a 

 massive covering of great strength and perfect flexibility, totally im- 

 pervious to water, and incapable of being destroyed by the minute an- 

 imalculae which exist in such abundance in warm latitudes, and which, 

 when the cable is not protected against their attacks, eat every atom 

 of hemp, as in the case of the cable laid between Toulon and 

 Algiers." 



Another important fact is stated, that wire varies greatly as much 

 as fifty or sixty per cent. - - in its capacity for conducting electricity. 

 The cable for the Persian Gulf is so well selected, and so well protect- 

 ed by gutta percha and compound, that the loss by leakage is scarcely 

 appreciable by the most delicate instruments. To such minute per- 

 fection has the system of testing adopted by the engineers been carried, 

 that the loss of one thousand-millionth part of the current by leakage 

 would be detected and estimated. The cost of this submarine section 

 will exceed $1,500,000. 



