1GO ANNUAL OF SCIENTIFIC DISCOVERY. 



could a signal from either station fail to traverse both parts of the 

 circuit at that station before passing on to the other. 



Since my former investigation (Proc. Amer. Assoc. Adv. Sci., 

 1850, p. 71 ; Am, Jour. Sci. xi., 67, 154) the progress of science 

 has thrown light upon many points which were then subjects of 

 doubt or of individual opinion. The condition of an open galvanic 

 circuit is now almost universally conceded not to be essentially 

 different from that of an interrupted conductor to an electrical 

 machine. The velocity of a current is also known to be de- 

 pendent upon its quantity, and therefore generally upon its 

 intensity, as well as upon the resistance of the conductor. But it 

 appears questionable whether the law is as simple as has been 

 supposed by some, who have regarded the velocity as inversely 

 proportional to the capacity of the conductor multiplied by its 

 resistance, and, therefore, in a homogeneous conductor to the 

 square of the length. For the problem, as it now presents itself, 

 does not pertain so much to the time for transmission of a given 

 signal, as to the time for its transmission with a certain force, 

 depending on the sensitiveness of the receiving apparatus; since 

 the electrical impulse or disturbance consists of a continuous 

 series of molecular influences which propagate themselves in 

 every possible direction according to the inverse ratio of their 

 several resistances. And the form of the conductor, as well as 

 other conditions, may essentially modify the time requisite for the 

 attainment of the prescribed force at the other extremity of the 

 line. A current may thus be temporarily established in part of 

 an open circuit, continuing until the battery and conductors have 

 attained an electrostatic equilibrium. The time required for 

 attaining this equilibrium depends of course simply on the ca- 

 pacity and form of the conductors, and on the energy of the 

 battery ; but the first electrical impulse may reach the most re- 

 mote point of the circuit before a portion nearest the battery has 

 received its full charge. Similarly, in a closed circuit, the distant 

 extremity of the line may well be supposed to perceive some 

 slight electrical disturbance from a signal before its full force is 

 manifested at intermediate points, so that a signal might be re- 

 ceived with a delicate galvanometer at the farther extremity, 

 before it could be recognized upon an electro-magnet at half the 

 distance. And this, too, apart from any consideration of increas- 

 ing intensity in the electromotor. 



The circuit formed by the two cables might, although broken 

 at Valencia, thus serve to establish what would practically be a 

 momentary current at Newfoundland when the battery at that 

 station was introduced, deflecting the galvanometer there for an 

 instant, and the change of statical condition in the cables at 

 Valencia would thereupon be manifest to the electroscope. Bat 

 the closure of circuit at Valencia would be accompanied by in- 

 stantaneous deflection of the galvanometer, with corresponding 

 insensibility of the electroscope. Thus a signal given by closing 

 or interrupting an insulated circuit at any point is instantaneously 

 transmitted from that point in both directions and at full speed ; 

 but the interval before it attains its total force at any other point 



