A RETROSPECT OF WIRELESS 
COMMUNICATION. 
BY 
SIR OLIVER LODGE, F.R.S. 
As one gets older people seem to think that one’s duty is to be an historian of the 
times during which one has lived. Unfortunately I have not been trained as an 
historian, and am therefore incompetent to do more than just trade upon my 
reminiscences, which are liable to be rather one-sided and not to satisfy the conditions 
for serious and reliable history without prejudice or favouritism. It has been 
suggested that I speak on the History of Wireless Telegraphy, under the title ‘A 
Retrospect of Wireless Communication.’ 
Looking back, then, over my lifetime, the first item to attract my attention was 
a paper on ‘ Transient Currents’ written by Lord Kelvin (as Sir William Thomson) 
in 1853, wherein he gave the theory of electric oscillations in a masterly manner 
considering that the idea of self-induction was not then born. He knew, however, 
that an electric charge could be stored in a condenser, after the same fashion as energy 
is stored in a bent or coiled spring, so that the condenser received and stored up 
electric energy, which it would subsequently give out when released. That was the 
first step. He knew, moreover, that the discharge would constitute an electric 
current, and that every electric current was surrounded by a magnetic field, which 
would confer upon it something akin to inertia or momentum ; so that, like a loaded 
spring, it would not only recoil when released, but would overshoot the zero mark 
and reverse of itself, swinging like a loaded pendulum first on one side the zero, then 
on the other; so that the discharge was not a flow in one direction only, but an 
oscillating or alternating flow, first in the positive, then in the negative direction. 
The magnetic field would thus prolong the discharge until the energy was finally 
wiped out; and the spark, if examined in a rotating mirror (as Feddersen examined 
it twenty years later) would be seen to be not a single luminosity, which would be 
drawn out into a uniform band, but would be a succession of luminosities or a beaded 
band, each band corresponding to a half swing. Kelvin did not attempt this experi- 
mental verification, but he went on with the theory. 
The elastic recoil or strength of the spring varies inversely with the capacity of 
the condenser. The smaller the condenser, the stiffer the spring; so that with a 
large condenser the oscillations would be fairly slow ; not really slow, but something 
comparable to a thousand or a hundred a second, something which could be made to 
give a musical note, if the capacity were very large. I exhibited this musical note 
at the Royal Institution many years afterwards in what I called a ‘ whistling spark.’ 
The noise of such a spark, instead of being a crack, was a whistle, whose pitch could 
be brought down to reach the tones of the voice, and indeed lower still. The rate of 
swing depends not only on the capacity of the condenser; it depends also on the 
load or inertia of the discharging circuit. It depends on what we now call self- 
induction, but which then Kelvin spoke of as ‘ the electro-dynamic capacity of the 
discharger.’ There was the electrostatic capacity of the charged condenser, and the 
electrodynamic capacity of its discharging circuit. The two co-operated so as to 
produce the swing, and the rate of swing depended on both equally, and could be 
calculated exactly. This theory Sir Richard Glazebrook and I subsequently verified, 
many years afterwards, in the Cavendish Laboratory, Cambridge, in the ’nineties of 
last century, the result being published in the Stokes Memorial Volume. 
The discharger not only had magnetic induction, it also had resistance, and Kelvin’s 
theory showed that if the resistance was above a certain amount, the oscillations would 
be quenched prematurely. There was a critical resistance at which they would be 
