"WIRELESS TELEGRAPHY. 
129 
Another point which no doubt will be of considerable interest to 
members of this Institution is how far secrecy can be maintained in 
this method of communication. If you erect a vertical wire and send 
signals through it, auy person who chooses to erect another wire any¬ 
where within the radius over which the signals can be transmitted, 
and to provide suitable apparatus can read your messages. Now when 
Mr. Marconi first introduced this system he expressed the opinion that 
it would be possible by suitably tuning the transmitters and receivers 
to overcome this difficulty. I fear, however, that with ordinary ver¬ 
tical wires this will be almost impossible, for it is found that instead of 
using two vertical conductors of the same height two of widely differ¬ 
ing dimensions giving the same product are used and equally good sig¬ 
nals are obtained. On looking at the question theoretically there appears 
to be no reason to expect a different result. Captain Brett explained 
how a series of surgings were set up on making contact between the 
induction coil and the transmitter. Now the apparatus that gives the 
largest number of surgings for each single original impulse consists 
chiefly of a Leyden jar with two short wires separated by an air gap to 
complete the circuit. It has been calculated that in a system of this 
kind, for one impulse of the coil there are 30 or 40 surgings in the 
oscillator. If another Leyden jar similarly fitted be placed in the 
neighbourhood of and within 2 or 3 feet of the former, and the two 
be carefully tuned, then on exciting the first or oscillator an overflow 
discharge is observed in the second or resonator. For this purpose 
tuning is absolutely imperative. With an oscillator of the ftighi type 
fitted with short horizontal wings, it is generally considered that only 
three or four surgings occur for each original impulse. Now with the 
three or four surgings it is still necessary to tune in order to transmit 
over the longest possible distance, but for shorter ranges, signals can 
be received even if the two circuits are not in tune. When a long ver¬ 
tical wire, however, is used there is every reason to believe that the 
surgings are reduced to one oscillation. Now if we consider the effect 
of resonance say on two stretched wires or strings, when one is put in 
continuous vibration, each vibration emits an impulse which is propa¬ 
gated through the air on to the second wire, and when the two are in 
unison these impulses are cumulative in their effect so that the latter 
responds to and repeats the original one. If, however, the two wires 
are not in tune the tendency of some impulses to increase the swing of 
the secondary wire is checked by subsequent ones in the opposite 
phase, and either the secondary gives no note at all, or perhaps an 
intermittent and irregular one. If, however, it were arranged that 
one single excursion or vibration only were imparted to the primary 
string that impulse would be conveyed through the air and would 
affect any other string irrespective of its length, and I think that 
action takes place when vertical wires are used for Hertzian radiation, 
because whether the oscillation and resonator are absolutely in tnne or 
not—you can always get the latter to respond to the former. There¬ 
fore it seems to me quite hopeless to expect to get secrecy by mere 
tuning when working with a system of vertical wires alone. There is 
