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SCIENCE. 



[N. S. Vol. VII. No. 180. 



experimenters have employed a series of 

 balls immersed in oil to generate the waves, 

 but Marconi's esperience is that the simpler 

 arrangement he now employs is just as effi- 

 cient. The receiving instruments consist of 

 a coherer, a relay and a Morse printer. 

 The coherer, the function of which is to de- 

 tect the presence of the electric waves that 

 travel through space from the sending sta- 

 tion, is a short piece of glass tubing into 

 which are sealed two silver pole-pieces. 

 Between these there is a narrow space con- 

 taining silver and nickel filings, and the 

 whole is exhausted of air, not because a 

 vacuum directly favors the sensitiveness of 

 the instrument, but to prevent oxidation of 

 the filings, which, of course, impairs their 

 conductivity. These pole-pieces are in- 

 cluded in an electrical circuit with the re- 

 lay and a single cell, and in addition one of 

 them is connected with the external con- 

 ductor and the other with the earth. 

 Normally the coherer does not conduct a 

 current. But, by virtue of some action 

 which is not yet fully undez-stood, under the 

 influence of an electric wave this condition 

 is altered and a current enabled to pass 

 through the filings between the pole-pieces. 

 The armature of the relay is then attracted 

 and the Morse printer or other suitable 

 receiving instrument brought into action. 

 Thus the signal is begun, but it has also 

 to be ended if the system is to be of practi- 

 cal use. The conductivity of the coherer 

 does not, as might perhaps be expected at 

 first sight, cease with the cessation of the 

 electric wave that established it, but persists 

 indefinitely so long as the instrument is 

 not disturbed. The least mechanical shock 

 or vibration, however, is suf&cient to de- 

 stroy it and to bring the coherer back to its 

 original non-conducting condition. Hence 

 Marconi provides on the relay circuit an 

 electrical tapper, which by keeping the 

 coherer in a state of constant vibration 

 breaks down its conductivity as soon as it 



is established. The method of working is 

 therefore as follows : If the operator at 

 Bournemouth wishes to send a message to 

 Alum Bay he connects his outside con- 

 ductor with his induction coil, at the same 

 time disconnecting it from the coherer. 

 Then by means of the key he puts his coil 

 into operation for long and short periods 

 corresponding to the dashes and dots of 

 the Morse code, thus exciting in the out- 

 side conductor groups of electric waves. 

 Some of these fall upon the outside conduc- 

 tor at Alum Bay and convert the coherer 

 there into a conductor ; the relay circuit is 

 immediately closed and the Morse instru- 

 ment begins to print. Of course, during the 

 transmission of one dash the circuit of the 

 coherer is made and broken many times, but 

 the printing instrument treats the quick suc- 

 cession of short currents as a single long 

 one. The rate at which messages are sent 

 in this way is not very great, but it is only 

 fair to say that no efforts have been made 

 to attain speed. The intention has rather 

 been to demonstrate that signals can be sent 

 with accuracy and certainty over a consider- 

 able distance without conducting wires. 



A number of experiments have also been 

 carried out between Alum Bay and a ship 

 cruising about between the Isle of Wight 

 and Swanage. In every case communica- 

 tion was easily maintained, whether the 

 ship was moving forwards or backwards or 

 swinging round. Nor was the working of 

 the apparatus adversely affected by bad 

 weather. On the contrary, it seemed to act 

 most freely in fog, rain or wind, and was 

 at its work on fine, clear, still days. These 

 facts suggest that an early practical appli- 

 cation of wireless telegraphy might be ad- 

 vantageously found in the establishment of 

 communication between the shore and out- 

 lying lighthouses and light ships. No really 

 satisfactory way of attaining this desirable 

 end has so far been devised, and seeing that 

 wireless telegraphy can be perfectly well 



