CONQUEST OF TIME AND SPACE 



fected an improved coherer, which consisted of a 

 glass tube four millimeters in diameter with two 

 silver plugs connected with the wires of an electric 

 battery but separated within the tube by an inter- 

 space of about one millimeter, this space being partly 

 filled with metallic filings, 5 per cent, silver and 95 

 per cent, nickel. Marconi had discovered that if his 

 coherer had "one terminal attached to a metallic 

 plate, lying on the earth, or buried in it, and the 

 other to the insulated plate above the ground, it 

 would detect the presence of very feeble electric 

 waves." 



He had also discovered that he could advantageous- 

 ly produce electric waves of great carrying power 

 by the use of a large induction or spark coil with 

 spark balls placed a few millimeters apart, one ball 

 being connected with the earth plate and the other 

 with plates or wires insulated at the upper end and 

 raised into the air. He put the apparatus in opera- 

 tion with the aid of an ordinary telegraphic signal- 

 ling key placed in the primary circuit of the induc- 

 tion coil. When the key was pressed there was a 

 rush of electric sparks between the balls alternately 

 charging and discharging the elevated conducting 1 

 wires and creating electrical oscillations. The longer 

 or shorter pressure of the key varied the action of 

 this transmitter making possible the use of the reg- 

 ular Morse code. 



Electric waves sent out by such a transmitter 

 radiate into space, and their sequence of emission 

 in longer or shorter series in response to the pressure 

 of the telegraph key, is recorded by the receptive 



309 



