342 Mr. G-. Marconi. Magnetic Detector of Electric [June 10, 



changes necessarily cause induced currents in the windings, which 

 induced currents in their turn reproduce on the telephone with great 

 clearness and distinctness the telegraphic signals which may be sent 

 from the transmitting station. 



Should the magnet be taken away, or its movement stopped, the 

 receiver ceases to be perceptibly affected by the electric waves, even 

 when these are generated at very short distances from the radiator. 



This detector has been successfully employed for some time in the 

 reception of wireless telegraphic messages between St. Catherine's 

 Point, Isle of Wight, and the North Haven, Poole, over a distance of 

 30 miles, and also between Poldhu, in Cornwall, and the North Haven, 

 over a distance of 152 miles, of which 109 are over sea and 43 over 

 high land. It has also been ascertained that signals can be obtained 

 over these distances with the new detector when employing less power 

 at the transmitting station than is necessary if a reliable coherer be 

 substituted for the magnetic detector. I have had occasion to notice, 

 however, that the signals audible in the telephone are weakest when 

 the poles of the rotating magnet have just passed the core and are 

 increasing their distance from it, whilst they are strongest when the 

 magnet poles are approaching the core. 



Very good results have also been obtained by keeping the magnet 

 fixed, and using an endless iron rope or core of thin wires revolving on 

 pulleys (worked by a clockwork arrangement), which cause it to travel 

 through the copper wire windings, in proximity to a horse-shoe magnet, 

 or, preferably, two horse-shoe magnets with their poles close to the 

 windings, and with their poles of the same sign adjacent. In this case 

 the copper wire windings are separated from the iron by means of a 

 stiff, thin pipe of insulating material in order to prevent chafing of 

 the wires. With this arrangement the signals appear to be quite 

 uniform in strength. 



There appears to be a certain magnetic force which gives best results, 

 but different qualities of iron require different values. There would 

 also appear to be a particular speed of revolution for the magnets 

 employed which is more suitable than any other. I have obtained 

 good results when causing the magnets to revolve at the rate of one 

 revolution every 2 seconds, or, when using a moving core, by causing 

 it to travel at a speed of about 30 cm. in 4 seconds. 



Either iron or steel can be used for the cores or revolving rope, but 

 I have observed that by far the best effects are obtained when using 

 hard-drawn iron wires or iron wire that has been considerably stretched 

 or twisted beyond its limits of elasticity prior to its employment. 



I have used cores generally consisting of about thirty hard-drawn 

 iron wires of approximately 0*5 mm. in diameter, with a winding on them 

 made up of a single layer of silk-covered copper wire 0'019 cm. in 

 diameter and of a total length' of 2-4 metres. The other winding, con- 



