RECENT ELECTRICAL DISCOVERIES 117 



to communicate with any selected receiver to the 

 exclusion of all others. 



An electric generator supplies the source of elec- 

 tricity for operating an induction coil to transform 

 the low pressure into an alternating current of high 

 pressure. This charges the wire suspended from a 

 mast and the wire leading to the earth to a suffi- 

 cient potential to cause the opposite charges of elec- 

 tricity to rush together, thus forming a spark or 

 disruptive discharge through a small air gap; as a 

 result high potential currents surge to and fro 

 through the wires hundreds of thousands of times 

 per second. 



These high potential currents radiate electric 

 waves which are propagated as light waves and 

 spread out in every direction. It is said the whole 

 process of transmitting and receiving wireless mes- 

 sages is not unlike to the emission of light and 

 its reception by the retina of the eye. 



The reception of these waves is by means of a 

 vertical wire similar to that used in transmitting, 

 the difference being the wires at the terminals are 

 connected with metal filings inclosed in a small 

 glass tube called the coherer instead of the spark 

 gap. The electric waves impinge on the elevated 

 wire and are converted into electric oscillations, 

 which act on the filings, and an auxiliary circuit 

 registers the impulses on a ribbon of paper in read- 

 able Morse dots and dashes. The higher the ver- 

 tical or mast wires and the greater the number 

 of wires, the greater the wave length and the far- 

 ther the distance transmitted. 



Marconi in his first Atlantic tests employed kites 

 and balloons to carry the vertical wire so that 



