Dr. 0. Lodge on Electric Radiation. 53 



dence of this with linear oscillators ; the reason being, I sup- 

 pose, that the damping out of the vibrations is so vigorous that 

 all oscillations after the first one or two are comparatively 

 insignificant ; and very bad adjustment, or no adjustment at 

 all, will give you the benefit of all the resonance you can get 

 from such rapidly decaying amplitudes. The main reason of 

 the rapid damping is loss of energy by radiation. The " power" 

 of the radiation while it lasts is enormous, and the stock of 

 energy in a linear oscillator is but small. 



Leyd en-jar discharges in closed circuits die away more 

 slowly, and for them some approach to exact timing is essen- 

 tial, if a neighbouring circuit is to respond easily. 



In working with small oscillators it is essential that the 

 spark-knobs shall be in a state of high polish, else the sparks 

 will not be sufficiently sudden to give the necessary impetus 

 to the electrification of the conductors. 



Any hesitation or delay about the spark permits the potentials 

 of the knobs to be equalized by a gradual subsidence which is 

 followed by no recoil, just as a tilted beer-barrel may be let 

 down gently without stirring up the sediment by waves. The 

 period of a natural vibration is comparable to the time taken by 

 light to travel a small multiple of the length of the oscillator, 

 and hence not a trace of delay is permissible in the discharge 

 of a small conductor if any oscillations are to be excited by 

 means of it. Thus if an electrostatic charge on a conducting 

 sphere be disturbed in any sudden way, it can oscillate to and 

 fro in the time taken by light to travel 1 *4 times the diameter 

 of the sphere, as calculated by Prof. J. J. Thomson ; and 

 hence it is by no means easy to disturb a charge on a sphere 

 of moderate size except in what it is able to treat as a very 

 leisurely manner. Even on large spheres the oscillations 

 cannot be considered slow : thus an electrostatic charge on 

 the whole earth would surge to and fro 17 times a second. 

 On the sun an electric swing lasts 6| seconds. Such a swing 

 as this would emit waves 19 x 10° kilometres or twelve hundred 

 thousand miles long, which, travelling with the velocity of 

 light, could easily disturb magnetic needles* and produce 

 auroral effects, just as smaller waves produce sparks in gilt 

 wall-paper, or as the still smaller waves of Hertz produce sparks 

 in his little resonators, or, once more, as the waves emitted 

 by electrostatically charged vibrating atoms excite corre- 

 sponding vibrations in our retina. It may be worth while to 

 suspend at Kew a compass-needle with a natural period of 

 swing of 6'6 seconds, and see whether it resounds to solar 



* Cf. Mr. Oliver Heaviside, Phil. Mag. February, 1888, p. 152. 



