1902.] on the Progress of Electric Space Telegraphy. 205 



such as are employed for syntonic wireless telegraphy. The ends of 

 the other winding are connected to the terminals of a telephone or 

 other suitable receiving instrument. Near the ends of tbo core, or 

 in close proximity to it, is placed a horse-shoe magnet, which, by a 

 clock-work arrangement, is so moved or revolved as to cause a slow 

 and constant change or successive reversals in the magnetisation of 

 the piece of iron. I have noticed that if electrical oscillations of 

 suitable period be sent from a transmitter, rapid changes are effected 

 in the magnetisation of the iron wires, and these changes necessarily 

 cause induced currents in the windings, which in their turn repro- 

 duce on the telephone with great clearness and distinctness the 

 telegraphic signals which may be sent from the transmitting station. 

 Should the magnet be removed 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. 



I have had occasion to notice that the signals audible on 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's poles are approaching the core. 

 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 clock-work), which cause the iron to travel through 

 the copper wire windings, in proximity to, preferably, two horse-shoe 

 magnets with their poles close to the windings, care being taken that 

 their poles of the same sign are adjacent. This detector has been 

 successfully employed for some time in the reception of wireless tele- 

 graphic messages between St. Catherine's Point, Isle of Wight, and the 

 North Haven, Poole, over a distance of 30 miles, also between Poldhu, 

 in Cornwall, and Poole, in Dorset, over a distance of 152 miles, of 

 which 109 are over sea and 43 over high land. 



It would, no doubt, be possible to obtain signals by causing the 

 iron core to act directly on a telephone diaphragm, and in this case 

 the secondary winding could be omitted. This detector, as I have 

 already stated, appears to be more sensitive and reliable than a 

 coherer, nor does it require any of the adjustments or precautions 

 which are necessary for the good working of the latter. It possesses 

 a uniform and constant resistance, and, as it will work with a much 

 lower E.M.F., the secondaries of the tuning transformers can be made 

 to possess much less inductance, their period cf oscillation being 

 regulated by a condenser in circuit with them, which condenser may 

 be much larger (in consequence of the smaller inductance of the 

 circuit) than those used for the same period of oscillation in a coherer 

 circuit, with the result that the receiving circuits can be tuned much 

 more accurately to a particular radiator of fairly persistent electric 

 waves. Asa call, a coherer in circuit, with a relay working a bell, 

 can always be used, and if it is found possible to make the magnetic 

 detector record on a registering instrument (as to the possibility of 

 which the results of recent tests have left little doubt in my mind), 



