196 Mr. G. Marconi [June 13, 



experimental proof by Clerk Maxwell and Heinrich Hertz of the 

 identity of light and electricity, and the knowledge of how to pro- 

 duce and detect certain previously unkno^vn ether waves, made 

 possible this new method of communication. I think I am right in 

 saying that the importance of the discoveries of Maxwell and Hertz 

 was realised by very few, and even, perhaps, so recently as a year ago a 

 great number of scientific men would have hardly foreseen the advances 

 which have been made in so brief a time in the art of space telegraphy. 



The time allowed for this discourse does not permit me to describe 

 all the various steps which have made possible the results recently 

 obtained nor to describe the work of the numerous workers who have 

 contributed to the advance of the subject, but I hope it may be of in- 

 terest if I describe the various problems which have lately been solved, 

 and the very interesting developments which have taken place in my 

 own work during the last few months. I shall first briefly describe 

 my system as used in my early experiments six years ago, and after- 

 wards endeavour to explain the various improvements and modifica- 

 tions which have since been introduced into it. 



Ihe transmitter consists of a modified form of Hertzian oscillator, 

 the main feature of which is in having one sphere of the spark dis- 

 charger earthed, and the other connected to an elevated capacity area 

 or to a comparatively vertical wire. The two spheres are also con- 

 vected to the ends of the secondary winding of an induction coil or 

 transformer. When the key is pressed the current of the battery is 

 allowed to actuate the spark coil, which charges the spheres and the 

 uertical wire, which, when discharging, causes a rapid succession of 

 sparks to pass across the spark-gap. The sudden release caused by the 

 spark discharge of the electrical strain or displacement created along 

 certain lines of electric force through space by the charged wire 

 causes some of the electrical energy to be thrown off in the form of a 

 displacement wave in the ether, and, as a consequence, the vertical 

 wire becomes a radiator of electric waves. In this connection it is 

 interesting to remember that Lord Kelvin showed mathematically 

 more than forty years ago the precise conditions under which such a 

 discharge as we are considering would be oscillatory. It is easy to 

 understand how, by pressing the key for longer or shorter intervals, 

 it is possible to emit a long or short succession of impulses or waves 

 which, when they influence a suitable receiver, reproduce on it a long 

 or short effect, according to their duration, in this way reproducing 

 the Morse or other signals transmitted from the sending station. 



The receiver consists of a coherer (on the nature of which I hope 

 to make a few further remarks later) placed in a circuit containing 

 a local cell and a sensitive telej^raph relay actuating another circuit, 

 which works a trembler or decohererand a recording instrument. In 

 its normal condition the resistance of the coherer is infinite, or at 

 least very great, and the current of the battery cannot pass through 

 it to actuate the instruments, but when influenced by electric waves 

 the coherer becomes a comparatively good conductor, its resistance 



