RECENT ADVANCES IN WIEELESS TELEGRAPHY. 



137 



that any telegraph or telephone wire can be tapped, or the conversa- 

 tion going on through it overheard, or its operation interfered with. 

 Sir William Preece has published results which go to show that it 

 is possible to pick up at a distance on another circuit the conversa- 

 tion which may be passing through a telephone or telegraph wire. 



Up to the commencement of 1902 the only receivers that could 

 be practically employed for the purposes of wireless telegraphy were 

 based on what mav be called the coherer principle — that is, the 

 detector, the principle of which is based on the discoveries and 

 observations made by S. A. Varley, Professor Hughes, Calsecchi 

 Onesti, and Professor Branh\ 



Early in that year the author was fortunate enough to succeed in 

 constructing a j^ractical receiver of electric waves, based on a prin- 

 ciple different from that of the coherer. Speaking from the ex- 

 perience of its application for over two years to commercial pur- 

 jDOses, the author is able to say that, in so far as concerns speed of 

 working, facility of ad- 

 justment, reliability, and 

 efficiency when used on 

 tuned circuits, this receiver 

 has left all coherers or 

 anticoherers far behind. 



The action of this re- 

 ceiver is in the author's 

 opinion based upon the de- 

 crease of magnetic hystere- 

 sis, Avhich takes place in iron when under certain conditions this metal 

 is exposed to high frequency oscillations of Hertzian waves. 



It is constructed in the following manner and is shown in fig. 12. 



On an insulating sleeve surrounding a portion of a core, consisting 

 of an endless rope of thin iron wires, are wound one or two layers of 

 thin insulated copper wires. Over this winding insulating material is 

 placed, and over this again another longer winding of thin copper 

 w4re contained in a narrow bobbin. The ends of the windings nearer 

 the iron core are connected one to earth and the other to the elevated 

 conductor, or they may be joined to any suitable syntonizing circuit, 

 such as is now employed for syntonic wireless telegraphy. The ends 

 of the longer winding are connected to the terminals of a suitable 

 telephone. A pair of horseshoe magnets are conveniently disposed 

 for magnetizing the portion of the core surrounded by the windings, 

 and the endless iron core is caused to move continuously through the 

 windings and the field of the horseshoe magnets. 



This detector is and has been successfully employed for both long 

 and short distance work. It is used on the ships of the Koyal Navy 

 and on all trans-Atlantic liners which are carrying on a long-distance 



Fig. r. 



