250 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1913. 



might be left out. .Consider the frequency still further raised, say, 

 to 6,000 cycles, this " skin effect " of the conductor still further in- 

 creases until the copper in the interior of a circular wire of a con- 

 siderable size is now quite useless, and to get the advantage of such 

 copper we must, as it Avere, take it out or spread it in a number of 

 parallel wires spaced apart, or make the metal of the conductor 

 in the form of a long sheet or in the shape of a thin tube or a cage 

 of wires (fig. 13). This, in electrical terms, improves the con- 

 ductivity and reduces the opposition due to self-induction; the in- 

 ductance counter E M F. Let now the frequency be still further 

 increased to tens of thousands or hundreds of thousands of cycles 

 per second; then our conductor must necessarily become a still 

 thinner or a still more extended sheet. 



At the same time, if there are considerable differences of potential 



between the conductors 

 Fi^.l3. thus arranged, the ra- 



diation factor may at 

 last become verj^ im- 

 portant, so that if the 

 parts of the circuit are 

 far apart, free radia- 

 tion into sjDace may 

 dispose of a large frac- 

 tion of the energy sent 

 out. In the Hertzian 

 oscillator, deducting 

 that lost in the spark 

 gap, practically the 

 whole of the remain- 

 ing energy supplied is 

 radiated into space. 

 The wave frequency may be very many millions per second, and the 

 waves produced are in the nature of coarse light and heat waves. 

 Figure 14 exemplifies diagrammatically the fact that with very high 

 frequency waves a conductor carrying such waves will have surround- 

 ing it, if the space is unrestricted, magnetic systems of lines reversed 

 in direction with nodes between, the distance apart of these waves or 

 nodes being determined by the frequency in relation to the velocity 

 of light, each complete wave outside the wire occupying a length 

 equal to the velocity of light, 186.000 miles per second, divided by 

 the wave length or f requencj^ 



Figures 15 and 16 represent forms of Hertzian oscillator, consist- 

 ing of plates or spheres ah oi metal, separated b}'' a small spark gap 

 and charged in any suitable way, plus and minus with respect to 

 each other, and allowed to discharge across the gap. The charges 

 are then interchanged between a and b at a very high rate. 



