220 hertz's experiments. 



second, and it is expected thereby to produce ^\ aves of electric force 

 whose length will be less than a meter if they are propagated with the 

 velocity of light. It is proposed to do this by causing an electric charge 

 to oscillate backwards and forwards between two conductors, and 

 across an air gap between them. This oscillating (iharge is to be started 

 by charging the conductors, one positively and the other negatively, 

 until they discharge by a spark across this air gap. By making the 

 conductors small, and the distance the charge has to go from one to 

 the other small, the rate of oscillation of the charge can be made as 

 great as we require. If waves are produced by this arrangemenj:, we 

 can reflect them at the surface of a large conducting sheet, and then 

 loops and nodes will be produced where the incident and reflected waves 

 co-exist. The loops will be places where the alternating electric forces 

 are great, while at the nodes there will be no electric forces at all. In 

 order to detect wliere there are these alternating electric forces and 

 where there are none, it is proposed to use either ai single wire bent 

 nearly into a circle, with a very minute air-gap between its ends, or 

 elvse two conductors x)laced end to end, with a minute air gap between 

 their ends. In either case, if the natural period of vibration of a 

 charge on the single conductor, or on each of the conductors in the 

 second arrangement, is the same as the rate of alternation of the elec- 

 tric force we wish to detect, there may be sufticieiit electrification of 

 the neighboring ends to cause a spark across the minute air-gap. We 

 are thus in jiosscssion of a complete apparatus for determining whether 

 electric waves are produced, and what their wave length is. 



The experiment is conducted as follows: 



The two conductors which are to generate the waves are placed — say, 

 one above the other, so that the electric charge will run up and down 

 in a vertical line across the spark gap between them. They might be 

 placed horizontally or in any other line, but for definiteness of descrip- 

 tion it is well to suppose some definite position. We may call them A 

 and B. They are terminated in polished knobs, between which the spark 

 passes. A and B are connected with the termitials of a Euhmkortf 

 coil, or a Wimshurstor other apparatus by which a succession of sparks 

 may be conveniently made to pass from A to B. Before the spark 

 passes, A and 7> are being electrified, and when the spark occurs the 

 electricity on A rushes over to B, and part of it charges B, while the 

 electricity on B rushes across the spark and i)artly charges A, this 

 taking place alternately up and down. Each time there is less elec- 

 tricity, for some is neutralized during each oscillation by the opposite 

 charge; for energy is being spent, some in overcoming the resistance of 

 tlie spark gap, *'. e., in producing the heat developed there, and some in 

 ])roduc{ng electric waves in the surrounding medium. Thus the elec- 

 tric energy of the two oppositely charged bodies ^L and B is gradually 

 dissipated, and one way of describing this is to say that the two oppo- 

 site electric charges combine and neutralize one another. This whole 



