556 EVENING DISCOURSES. 
require the separate constants to be measured, nor need we know what each was; 
only their product entered into the expression. Experiments made abroad, in 
Germany, had indicated a way of determining this product; Maxwell bethought 
himself of another method, and proceeded to put it into practice in the laboratory of 
King’s College, London, where he was then a professor. He performed the experi- 
ment, worked out the result, and obtained a speed for the transmission of electro- 
magnetic waves very close to the velocity of light. It looked as if ether waves were 
just what we had been using all along for optical experiments and for arousing our 
sense of vision. We had been discussing whether ether waves were possible; they 
were familiar, only we didn’t know they were electromagnetic. 
All manner of theories of light had been tried in the early part of the nineteenth 
century—very ingenious theories, depicting the ether as a kind of elastic solid or 
jelly, in which the vibrations travelled at an immense pace. But none of these 
theories had been satisfactory. They covered the ground to a great extent, but they 
failed sooner or later. There were things we could not account for by any elastic 
solid theory. But Maxwell’s theory that light was not mechanical but was an electro- 
magnetic phenomenon, that its laws were ascertainable by electric and magnetic 
experiments, was a tremendous eye-opener. His book was published in 1873. The 
president of Section A of the British Association called attention to it, and we young 
people were all agog to understand this theory better, and if possible to verify it by 
actually producing ether waves electromagnetically. That was what set FitzGerald 
to work, and I have given you an indication of his results. 
I also set to work experimentally, and tried to produce the waves by the dis- 
charge of Leyden jars. No doubt I did produce them—that was easy enough; the 
thing was to detect them. The eye is useless for waves measured in metres; it can 
only deal with the excessively rapid vibrations that constitute light. We needed what 
Lord Kelvin called ‘an electric eye.’ We worked mainly with closed condensers— 
that is to say, things of which the opposite plates were near together—and tried to see 
if there was any sign of waves running along wires which were attached to such dis- 
charging condensers. In 1887 or ’8 I got the evidence in the form of nodes and loops 
characteristic of ether waves, reflected back on themselves at the terminal of the 
wire. But Heinrich Hertz in Germany, though not himself seeking to verify Maxwell’s 
theory, which had not attracted much attention on the Continent, but making experi- 
ments on the way in which electric force streamed out from a discharging conductor, 
arrived at a sensational result. He did not work with closed circuits. He took two 
plates, like the two coats of a Leyden jar, separated from one another as far as possible, 
and joined by a wire: in fact, he made what we now call a Hertz vibrator. It can 
hardly be called a condenser, but still it has capacity and self-induction, that is, the 
two ingredients necessary for an oscillation, and when the two surfaces were charged 
oppositely and sparked into one another, oscillations were set up, and waves were 
generated, as FitzGerald had perceived they would be. They were generated in 
space, however, because the electric field was spread out in space as well as the 
magnetic. They had such energy, these waves, that when they fell upon a conductor 
they caused it to emit little sparks. Such a thing as that we experimenters had not 
imagined possible. We had never thought that a luminous field would be strong 
enough to excite sparks when absorbed. FitzGerald might have thought of it if he 
had interpreted his expression in terms of energy numerically. He had not done that, 
none of us had done that, but he perceived the strength and beauty of Hertz’s result, 
and in 1888, at the British Association Meeting in Bath, he called the world’s 
attention to the fact that Maxwell’s electromagnetic waves had at last been produced ; 
not only produced, but detected, and detected by their extraordinary amount of 
energy sufficient to emit sparks. 
After that, progress was rapid. Hertz’s discovery was first understood and made’ 
notorious in this country. It never caught the ear of the public, it was not taken up 
by the newspapers, but it could not fail to arouse attention through the whole of the 
scientific world. Hertz showed that Maxwell’s theory would account for his radiation 
in every detail; he made a map of the process by which the radiation was generated 
in an electric oscillator, that is, he mapped out the lines of force during every phase 
of an oscillation—the beginning, the quarter of an oscillation, half of an oscillation, 
three-quarters, the complete—and these maps of lines of force were published in 
Nature when | translated his paper into that journal in February 1889. See vol. 39, 
p- 451. They could be shown in action on a kinematograph. 
