Things not generally Known. 



sand miles of the cable ! Each signal was registered at the end 

 of the cable in less than three seconds of time. 



The entire length of wire, iron and copper, spun into the 

 cable amounts to 332,500 miles, a length sufficient to engirdle 

 the earth thirteen times. The cable weighs from 19 cwt. to a 

 ton per mile, and will bear a strain of 5 tons. 



The Perpetual Maintenance Battery, for working the cable at 

 the bottom of the sea, consists of large plates of platinated sil- 

 ver and amalgamated zinc, mounted in cells of gutta-percha. 

 The zinc plates in each cell rest upon a longitudinal bar at the 

 bottom, and the silver plates hang upon a similar bar at the top 

 of the cell ; so that there is virtually but a single stretch of 

 silver and a single stretch of zinc in operation. Each of the 

 ten cells contains 2000 square inches of acting surface ; and 

 the combination is so powerful, that when the broad strips of 

 copper-plate which form the polar extensions are brought into 

 contact or separated, brilliant flashes are produced, accompa- 

 nied by a loud crackling sound. The points of large pliers are 

 made red-hot in five seconds when placed between them, and 

 even screws burn with vivid scintillation. The cost of main- 

 taining this magnificent ten-celled Titan battery at work does 

 not exceed a shilling per hour. The voltaic current generated 

 in this battery is not, however, the electric stream to be sent 

 across the Atlantic, but is only the primary power used to call 

 up and stimulate the energy of a more speedy traveller by a 

 complicated apparatus of " Double Induction Coils." Nor is 

 the transmission-current generated in the inner wire of the 

 double induction coil, and which becomes weakened when it 

 has passed through 1800 or 1900 miles, set to work to print or 

 record the signals transmitted. This weakened current merely 

 opens and closes the outlet of a fresh battery, which is to do 

 the printing labour. This relay-instrument (as it is called), 

 which consists of a temporary and permanent magnet, is so sen- 

 sitive an apparatus, that it may be put in action by a fragment 

 of zinc and a sixpence pressed against the tongue. 



The attempts to lay the cable in August 1 857 failed through 

 stretching it so tightly that it snapped and went to the bottom, 

 at a depth of 12,000 feet, forty times the height of St. Paul's. 



This great work was resumed in August 1858 ; and on the 

 5th the first signals were received through two thousand and 

 fifty miles of the Atlantic Cable. And it is worthy of remark, 

 that just 111 years previously, on the 5th of August 1747, Dr. 

 Watson astonished the scientific world by practically proving 

 that the electric current could be transmitted through a wire 

 hardly two miles and a half long* 



* These illustrations have been in the main selected and abridged from papers 

 in the Companion to the Almanac, 1858, and the Penny Cyclopaedia, 2d supp. 



