MIRACLES OF SCIENCE 



coherer, which, as we have seen, transmits the electric 

 current of its own circuit only while the Hertzian 

 waves beat upon it, and which is automatically re- 

 stored to its condition of non-conductivity by the 

 apparatus that taps gently against the tube. 



Such was the essential character of the apparatus 

 through which Signor Marconi made his conquest 

 of the ether. The modifications that have since been 

 made pertain to the production of more powerful 

 transmitters on one hand and more sensitive receiv- 

 ers on the other. They include partially successful 

 attempts to send the electric waves in a desired di- 

 rection; and magnetic receivers of greater sensitive- 

 ness than. the metal filing coherer. The most strik- 

 ing amplification of the method, however, is the at- 

 tempt to adapt the apparatus to the transmission 

 of the human voice; to perfect, in other words, a 

 wireless telephone. 



In this effort a large measure of success has been 

 attained, in particular by the American, Dr. Lee De 

 Forest, who in 1907 perfected an instrument with 

 which he could transmit the music of a phonograph 

 between stations situated in different city blocks. A 

 few weeks later he was able to report by voice the 

 results of yacht races at a distance of about four 

 miles. In the autumn of the same year his instru- 

 ments were installed on the American fleet of war 

 vessels on their trip round the globe, and kept the 

 vessels in verbal communication with each other, 

 in storm and calm, during the entire voyage. A year 

 later it was reported that messages had been sent and 

 received at a distance of over 500 miles, and that a 



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