RADIO COMMUNICATION 253 



the primary circuit is shown at (&). An induction coil and spark 

 gap for transforming the low-voltage direct current into a high- 

 voltage, high-frequency oscillating current are shown at (i) and 

 (sg). The antenna or aerial conductor is shown at (a) and the 

 other side of the spark gap is grounded at (g). 



When the primary circuit is closed, sparks will jump across 

 the gap (Fig. 112), and since these are in reality electrical dis- 

 charges of very high frequency they will set up in the antenna 

 and ground circuit a very high frequency electrical current. 

 This current will set the ether surrounding the antenna into vibra- 

 tion, and thus will radiate into space long and short series of vibra- 

 tions corresponding to the dots and dashes of the telegraph code. 



It is in the circuit 

 consisting of antenna, i 



spark gap, and ground ( uHO 

 connections that the 

 radio vibrations origi- 



nate. A condenser f 



which will withstand 



high potential electrical FlG " II2 -~ A spark gap 



charges of several thousand volts may be connected across the 

 spark gap, and then a coil of heavy wire with adjustable con- 

 nectors may be included in the antenna circuit. With these 

 additions we have a typical radio-frequency oscillating circuit 

 as is shown in the second diagram (Fig. 113, p. 254). 



The condenser consists of two sets of sheets of tinfoil or other 

 good conductor, the sheets of one set alternating with those of 

 the other, and each sheet is carefully insulated from its adjacent 

 fellows. The ends of the fine wire on the transformer each attach 

 to one of these two sets. One set also fastens to a wire that runs 

 to the aerial, and that also branches to connect with one of the 

 metallic knobs of the spark gap; the other set fastens to a wire 

 that runs to the ground, and that branches to the other knob of 

 the spark gap. This spark gap is made of two adjustable metal- 

 lic rods, mounted close together in the same straight line. Each 



