254 The Mathematical Electricians of the 



This simple result may be regarded as the beginning of the 

 theory of electric oscillations. 



Thomson was at this time much engaged in the problems 

 of submarine telegraphy; and thus he was led to examine 

 the vexed question of the " velocity of electricity " over long 

 insulated wires and cables. Various workers had made 

 experiments on this subject at different times, but with 

 hopelessly discordant results. Their attempts had generally 

 taken the form of measuring the interval of time between the 

 appearance of sparks at two spark-gaps in the same circuit, 

 between which a great length of wire intervened, but which 

 were brought near each other in order that the discharges 

 might be seen together. In one series of experiments, 

 performed by Watson at Shooter's Hill in 1747-8,* the circuit 

 was four miles in length, two miles through wire and two 

 miles through the ground ; but the discharges appeared to be 

 perfectly simultaneous; whence Watson concluded that the 

 velocity of propagation of electric effects is too great to be 

 measurable. 



In 1834 Charles Wheatstone,f Professor of Experimental 

 Philosophy in King's College, London, by examining in a 

 revolving mirror sparks formed a,t the extremities of a circuit, 

 found the velocity of electricity in a copper wire to be about 

 one and a half times the velocity of light. In 1850 H. Fizeau 

 and E. GounelleJ experimenting with the telegraph lines from 

 Paris to Eouen and to Amiens, obtained a velocity about one- 

 third that of light for the propagation of electricity in an iron 

 wire, and nearly two- thirds that of light for the propagation 

 in a copper wire. 



The first step towards explaining these discrepancies was 

 made by Faraday, who early in 1854 showed experimentally 

 that a submarine cable, formed of copper wire covered with 



* Phil. Trans, xlv (1748), pp. 49, 491. 

 t Phil. Trans., 1834, p. 583. 

 ; Comptes Rendus, xxx (1850), p. 437. 



Proc. Roy. Inst., Jan. 20, 1854: Phil. Mag-., June, 1854: Exp. Res. iii, 

 pp. 508, 521. 



