1902.] on the Progress of Electric Space Telegraphy. 19? 



falling to between 100 and 600 ohms. This allows the current from 

 the local cell to actuate the relay, which in turn causes another 

 stronger current to work the recording instrument and also the tapper 

 or decoherer, which is so arranged as to tap or shake the coherer, and 

 in this way restore its sensitiveness. The practical result is that the 

 circuit of the recording instrument is closed for a time equal to that 

 during which the key is pressed at the transmitting station, and in 

 this way it is possible to obtain a graphic, acoustic or optical repro- 

 duction of the movements of the key at the sending station. One 

 end of the tube, or coherer, is connected to earth and the other to an 

 insulated conductor, preferably terminating in a capacity area similar 

 in every respect to the one employed at the transmitting station. 



I first noticed that by employing similar vertical rods at both 

 stations, it was possible to detect the effects of electric waves, and in 

 that way convey the intelligible alphabetical signals over distances 

 far greater than had previously been believed possible, and by means 

 of similar arrangements distances of transmission up to about 100 

 miles were obtained. 



It was soon, however, realised that so long as it was possible to 

 work only two installations within what I may call their sphere of 

 influence, a very important limit to the practical utilisation of the 

 system was imposed. Without some practical method of tuning 

 the stations it would have been impossible to work a number in 

 the vicinity of each other at the same time without interference 

 caused by the mixing of messages. The new methods of connection 

 which I adopted in 1898 — i.e. connecting the receiving vertical wire 

 or aerial directly to earth instead of to the coherer, and by the intro- 

 duction of a proper form of oscillation transformer in conjunction 

 with a condenser so as to form a resonator tuned to respond best to 

 waves given out by a given length of aerial wire — were important 

 steps in the right direction. I referred at length to this improvement 

 in the discourse which I had the honour to deliver at this table on 

 February 2, 1900. I had, however, realised at the time that one 

 great difficulty in the way of achieving the desired effects was caused 

 by the action of the transmitting wire. A straight rod in which 

 electrical oscillations are set up forms, as is well known, a very good 

 radiator of electrical waves. In all what we call good radiators elec- 

 trical oscillations set up by the ordinary spark-discharge method cease 

 or are damped out very rapidly, not necessarily by resistance, but by 

 electrical radiation removing the energy in the form of electric waves. 



It is a well-known fact that when one of two tuning forks 

 having the same period of vibration is set in motion, waves will form 

 in the air, and the other tuning fork, if in suitable proximity, will 

 immediately begin to vibrate in unison with the first. In the same 

 way a violin player, sounding a note on his instrument, will find a 

 response from a certain wire in a piano, near by, that particular wire, 

 out of all the wires of the piano, happening to the only one which 

 has a period of vibration identical with that of the musical note 



