214 hertz's experiments. 



to give some lesult if the waves are propagated at tliis enormous rate. 

 The distance from a node to a node is half the distance a wave travels dur- 

 ing a vibration. If we can produce vibrations at the rate of 300,000,0(10 

 per second, a wave would go 1 metre during a vibration, so that, with 

 this enormous rate of alteinatiou, the distance from node to node would 

 be 50*^^'"* We might expect to be able to work on this scale very 

 well, or even on ten times this scale, /. e., with alternations at the rate 

 of 30,000,000 per second, and 5 metres from node to node, but hardly 

 on a much larger scale than this. It almost takes one's breath away 

 to contemplate the i)roduction of vibrations of this enormous rapidity. 

 Of course they aie very much slower than those of light; tbese latter 

 are more than a million times as rapid; but 300,000,000 per second is 

 enormously more rapid than any audible sound, about a thousand 

 times as fast as the highest audible note. A short bar of metal vibrates 

 longitudinally very fast, but it would have to be about the thousandth 

 of a centimeter long in order to vibrate at the required rate. It would 

 be almost hopeless by mechanical means to produce electric alterna- 

 tions of this frequency. Fortunately there is an electric method of pro- 

 ducing very rapid alternate electritications. When a Leyden jar is 

 discharged through a wire of small resistance, the self-induction of the 

 current in this ware keeps the current running after the jar is dis- 

 charged, and re-charges it in the opposite direction, to immediately 

 dischargee back again, and so on through a series of alternations. This 

 action is quite intelligible on the hypothesis that electrifications con- 

 sists in a strained condition of the aether, which relieves itself by means 

 of the coiiductor. Just as a bent spring or other strained body, when 

 allowed suddenly to relieve itself, relieves itself in a series of vibra- 

 tions that gradually subside, similarly the strain of the ;ether relieves 

 itself in a series of gradually subsiding vibrations. If the spring 

 while relieving itself has to overcome fricticnuil resistance, its vibra- 

 tions will rapidly subside; and if the friction be sufticiently great, it 

 will not vibrate at all, but will gradually subside into its position of 

 equilibrium. In the same manner, if the resistance to the relief of the 

 strain of the medium, which is offered by the conducting- wire, be 

 great, the vibrations will subside rapidly, and if the resistance of the 

 wire be too great, there will not be any vibrations at all. 



Of course, quite independently of all frictional and viscous resistances, 

 ai vibrating spring, such as a tuning-fork that is producing sound-waves 

 in the air, which carry the energy of the fork away from it into the sur- 

 rounding medium, will gradually vibrate less aud less. In the same way, 

 quite independently o. the resistance of the conducting wire, we must 

 expect that, if a discharging conductor produces electric Maves, its 

 vibrations iiuist gradually subside owing to its energy being gradually 

 transferred to the surrounding' medium. As a consequence of this the 

 time that a Leyden jar takes to discharge itself in this way may be very 

 short indeed. It may i)erforni a good many oscillations in this very 



