NATURAL PHILOSOPHY. 163 



TRANSATLANTIC TELEGRAPH. 



In a recent communication to the Journal of the Frankln Institute, on 

 the subject of trans-telegraphic Atlantic communication, Dr. L. Turnbull, 

 well known for his acquaintance with telegraphic operations, presents the 

 following points respecting the consummation of this great enterprise : 



1st. " To find a time calm enough and a sea smooth enough to lay down 

 a telegraphic cable." In my own mind, this first difficulty can be over- 

 come as easily as the observations of Lieut, Berryman were made ; if times of 

 calm are found for such careful observations as he has conducted, by means 

 of a twine string so as to let down a cannon ball of sixty-four pounds, and 

 then raise a tube filled with shells and earth of the depths of the ocean, 

 we are almost certain a time calm enough and a smooth sea can be found 

 to stretch a wire from cable from land to land. 



The second difficulty is, a " wire long enough." On this point we have 

 accurate data to follow. The cable from Calais to Dover is twenty-four 

 miles long, and consists of four copper wires, through which the electric 

 currents pass, insulated by coverings of gutta-percha. These are formed 

 into a strand and bound round with spun-yarn, formings core or centre, 

 around which are laid ten iron galvanized wires of o-16th of an inch in 

 diameter, each welded into one length of 24^ miles, and weighing about 

 15 tons per mile. The rope weighs altogether about ISO tons. It formed 

 a coil of 30 feet diameter outside, ID feet inside, and 5 feet high, and was 

 made, in the short space of twenty days, by a machine invented for the 

 purpose. The transatlantic cable, if the machinery is multiplied and 

 sixteen machines are employed, could, we have little doubt, complete the 

 cable in six or seven months. 



The third difficulty is, " a ship big enough." This can be no difficulty ; 

 for if one would not do, twenty would. What is the objection to sending 

 it by trips, or in pieces ? Could it not be attached, as it was laid down, to a 

 buoy ? A vessel of 1,000 tons could surely carry 400 tons of coil, for our 

 cable would not exceed 12,000 tons. 



Another important matter to be determined is, to what extent a galvanic 

 current can be sent on an insulated wire. This has been also determined ; 

 for, in favorable states of the atmosphere, lines in this country have been 

 so insulated as to work in one circuit from 800 to 1,000 miles. The great- 

 est distance that any of the lines have ever worked in one circuit was 

 from Boston to Montreal, via New York, Buffalo, and Toronto a distance 

 of about 1500 miles. This was done when the earth was frozen and the 

 lines insulated by frost. The entire length of the telegraph line from Xew 

 York to New Orleans is 1,906 miles, via Charleston and Mobile ; and even 

 this distance has been worked in one circuit by the aid of an instrument 

 termed the connector, the effect of which is to cause one circuit to work 

 the other tlirough the entire series, thus producing a result similar to 

 working through, the entire line in one circuit 



