THE TELEGRAPH 329 



intervening space filled with metal filings. Under ordinary 

 conditions these filings do not conduct electricity, but when 

 they are acted upon by an electric wave, they change their 

 positions . and arrange themselves in such a way that an 

 electric current can pass through them. The connections 

 for a receiving instrument are shown in figure 136. When 

 the filings become affected by the electric waves, the current 

 from the battery B passes through and this operates a relay 

 M . When this relay is closed, a second circuit is brought 



FIG. 135. Wireless telegraph station at Glace" Bay. 



into action, including the battery 6, the tapper and the 

 telegraph sounder. This tapper is called the decoherer be- 

 cause, when it strikes the coherer, it breaks up the regular 

 arrangement of filings so that they cease to conduct elec- 

 tricity. The tapper works like an electric bell. In this 

 same circuit is placed the recording instrument, which is 

 similar to a regular telegraph sounder. In order that tht 

 sounds may be more easily heard, listening attachments are 

 placed over the ear. 



The Morse code of telegraph signals is used. In this case, 

 however, the dash becomes a series of rapid dots very close 



