1907.] 0)1 Recent Contributions to Electric Wave Telegra,phy. 670 



some reasons for considering that they do possess an actual physical 

 existence, and that they are a necessary part of the mechanism of 

 atoms and electrons.* They have a strong resemblance in many 

 ways to the vortices or vortex lines, which can be created in a fluid. 

 Moreover, just as vortex lines in a fluid can be self-closed or endless, 

 or else terminate in little whirlpools on the free surface of the liquid, 

 so lines of electric force can form either closed loops, or else have 

 their ends terminating on opposite charges of electricity, that is, on 

 an electron at one end and the positive charge of an atom, whatever 

 that may be, at the other end. Suppose, then, that the rod is 

 suddenly connected to the earth at the bottom end by allowing it to 

 spark to the earth. Its electric charge rushes out, that is, the excess 

 or deficit of electrons on its surface disappears, and this movement of 

 electricity constitutes an electric current flowing into or out of the rod 

 from the earth. The electrons, however, possess inertia or mass, 

 hence when they rush out of the rod into the earth they not only 

 discharge it, but overdo it, and leave the rod with a positive charge. 

 They then rush back again, and the process repeats itself, and we 

 thus obtain a rapid ebb and flow of electricity into and out of the 

 wire, called a series of electric oscillations. Each rush, however, 

 is feebler than the last, and therefore the oscillations decay away or, 

 as it is termed, are damped. The energy represented by the initial 

 charge is frittered away, partly owing to collisions of the electrons 

 and atoms in the rod and spark during the movement, and partly 

 because the electron radiates or communicates its kinetic energy to 

 the medium when it is accelerated or retarded. 



We have next to attend to the effects taking place outside the rod 

 or antenna. As the negative charge disappears from the rod owing 

 to the removal of the excess of free electrons from its surface the ends 

 of the lines of electric force which abut on it and stretch between it 

 and the earth glide downwards along the rod and end by forming a 

 semi-loop of electric force or strain with its ends or feet resting on 

 the earth (see Fig. 2). This arises from the facts that the lines of 

 force exercise a lateral pressure on each other, whilst lengthways they 

 •are in a state of tension, and also that lines of electric strain cannot 

 exist inside a conductor such as a spark. Hence when the spark 

 happens, the hues which a moment ago stretched across the spark gap 

 disappear. There is then an unbalanced pressure on the remaining 

 lines which are thus squeezed in towards the gap and deformed, so 



* Cf. Faraday. " Experimental Researches in Electricity," vol. iii. 

 series xxix., 3273, 3297, and 3299. " On Physical Lines of Magnetic Force." 

 Faraday used the expression physical line of force to denote their concrete 

 reality as distinguished from a mere geometrical conception. Also in his 

 paper, " Thoughts on Ray Vibrations," Phil. Mag., ser. 3, vol. xxviii,, 1846, he 

 considers that light may be a vibration propagated along lines of force. See 

 also J. J. Thomson, " Electricity and Matter," p. 63, for an argument for the 

 physical reality of lines of electric force drawn from the ionisation of gases by 

 Rontgen rays. 



