The Act of Creation (96 page)

In the domain of inanimate matter, the Voltaic battery, inspired
by Galvani's frogs, led to a parallel synthesis of electricity and
chemistry. The battery gave the experimenters for the first time ample
supplies of electric current -- which neither the friction machines
nor the Leyden Jar had been able to do. It taught them not only that
the chemical interaction of metals produced electricity; but also
that an electric current sent through certain chemicals led to their
decomposition. In 1806 Davy tentatively suggested that chemical affinity
had an electrical basis. But nearly a century had to pass until, in 1897,
Thompson discovered that a certain type of electrical discharge -- the
so-called cathode rays -- consisted of particles smaller than atoms; and
that in these particles 'matter derived from different sources such as
hydrogen, oxygen, etc. -- is one and the same kind, this matter being the
substance from which the chemical elements are built up'. [5] Thompson's
'elementary corpuscles' were later named 'electrons'.
But let me return for a moment to the Voltaic battery. The abundant flow
of current which it produced was so startling that it was at first doubted
whether this 'electric fluid' was the same kind of thing which came in
sparks out of the older contraptions. Comparison of their effects led to
the realization that the discharges of static electricity from a Leyden
Jar had a higher potential or tension, whereas the flow from the battery
had a low potential but carried a greater quantity of current. Thus the
distinction was made between the potential (voltage), roughly comparable
to the gradient of a river-bed, and the quantity of liquid (amperage) that
passed through it. But only fifty years later did Faraday realize that
the spark from a Leyden Jar could be regarded as a short-lived current;
then came Maxwell, who treated currents as moving charges, thus finally
unifying the two kinds of electricity: 'frictional' and 'Voltaic'.
In the meantime, however, that other grand synthesis got underway: the
unification of electricity and magnetism. There were several steps. The
first link was established in 1820 by the observation of Hans Christian
Oersted in Copenhagen that if an electric current flowed through a wire
in the vicinity of a magnetic compass, the needle was deflected and
turned into a position at right angles to the wire. The news created an
immediate sensation in Paris, where Ampère's excitable brain gave
off a spark bigger than any Leyden Jar: he realized in a single flash
that if an electric current produced a magnetic field, as the reaction
of the needle indicated, then all magnetic fields may be due to electric
currents -- that magnetism was a by-product of electricity. He let a
current run through a spiral coil inside of which he placed a steel
needle: it became magnetized, and the first electro-magnet was born.*
But how, then, was the 'natural magnetism' of loadstones to be explained,
which had no currents running around them? Ampère's answer was that
minute currents were circulating in coils inside the atoms of the
loadstone. These sub-atomic currents produced magnetic fields, which
tended to align themselves with the magnetic field of the biggest
loadstone, the earth. The theory at the same time dispensed with the
necessity of explaining magnetism by the physical action of poles;
it was perhaps the boldest and most surprising idea in this whole
development. Unfortunately, Ampère's contemporaries were not 'ripe'
for it. To quote D. L. Webster:

Scientists should have reacted to this surprise better than they did --
but scientists are human. The philosophical principle of parsimony in
hypotheses should have been their guide. Instead their guide seems to
have been habit. Parsimony would have dictated as follows:
1. Whatever we believe about magnets, we must recognize currents in
wires as currents.
2. The pole theory of magnets requires us to believe in two types of
field producers, poles and currents, whereas Ampère's theory requires
only currents.
3. The pole theory requires two very different sets of laws for magnetic
fields, one for fields due to poles and the other for fields due
to currents, whereas Ampère's theory requires only one set of laws.
4. Therefore, we shall follow Ampère.
But poles were treated as real for nearly another century. [6]

Yet Ampère's idea was never entirely forgotten. Maxwell compared
Ampère's sub-atomic coils to miniature spinning-tops which always tend
to preserve the direction of their axes; he tried to magnetize a piece
of iron by rotating it fast. In 1913, when Niels Bohr invented his
model of the atom as a miniature solar system, it was thought that the
orbital motions of the electrons round the nucleus provided the
Ampèrean circuits. This turned out to be part of the truth; but the
principal source of magnetism was found to be, even more surprisingly,
a spinning motion of the electrons round their own axes. An electron,
of course, can hardly be said to have an axis since it is now regarded as
something in the nature of a blur; but mathematically the model worked,
and that is all one can ask for in the present state of physics. A
century after Oersted, magnetism and electricity were finally reduced
to a common source.
But I have been anticipating the happy end. The next stage, after
Ampère had shown that an electric current will produce a magnetic
field, was the discovery by Faraday (in 1831) that magnetism could be
'directly converted into electricity' by moving magnet and conducting
coil relative to each other.* This led to the invention of the dynamo,
and later of the electric motor; but we are concerned with theory,
not with the ubiquitous applications of electric energy.
Faraday, as we know, was a visualizer, who saw the universe patterned
by lines of force -- like the familiar diagrams of iron filings grouped
round a magnet. James Clark Maxwell, who inaugurated the post-Newtonian
age in physics, was a super-visualizer. He took Faraday's imaginary
lines of force and put them into imaginary tubes carrying a fluid;
then he abolished the spaces between the tubes so that they became
'mere surfaces, directing the motion of a fluid filling up all space'
-- the ether. Next, he applied to this model the rules of a game which
bore no relation at all to electro-magnetism -- hydro-dynamics, with
its vortices and eddies and changing pressures.** One conclusion which
emerged from this imaginary operation was that all changes in electric
and magnetic force (for instance, those caused by an oscillating circuit)
sent waves spreading through space; and that these waves had the same
transverse character, and the same speed, as light. 'We can scarcely
avoid the inference', he wrote in a monumental sentence, 'that light
consists in the transverse undulations of the same medium which is the
cause of electric and magnetic phenomena.'
Thus after electricity and magnetism had been united, both were now
united to light. Electro-magnetic radiations came to be regarded as
rapid alternations of electrical and magnetic stresses in space, where
each change in the electric stress gives rise to a magnetic stress,
which again gives rise to an electric stress and so on. Soon the range
of these radiations was shown to comprise not only the visible spectrum
between the ultra-violet and the infra-red of radiant heat, but to extend
to the ultra-short gamma rays of radioactivity, and to the kilometre-long
waves used in radio-communication.
Perhaps the most fascinating aspect of Maxwell's genius is that as
soon as he had worked out the mathematical formulation of his theory,
he discarded the model by means of which he had reached it. It was as if
a man, after climbing a ladder to get a free view over his surroundings,
had kicked out the ladder from under him, and remained freely suspended
in the air. Gone were the tubes, the vortices, the ether; all that
remained were 'fields' of an abstract, non-substantial nature, and the
mathematical formalism which described the propagation of real waves
in an apparently non-existent medium. It was the great turning point
in physical science, when the aspiration to arrive at intelligible,
mechanical models was abandoned. This renunciation, born of necessity,
soon hardened into dogma -- a secular version of the Commandment 'Thou
shalt not make unto thee any graven image' -- of gods or atoms.*
The transition from model-making to mathematical abstraction is strikingly
illustrated by the fact that Maxwell himself left it to others (to
Heinrich Rudolph Herz, as it came to pass) to give empirical proof of
his electro-magnetic waves. As Crowther wrote:

The General Equations of the Electro-magnetic Field were more real to
him than material phenomena he could know in the laboratory. Physicists
have often wondered why Maxwell made no attempt to prove experimentally
the existence of electro-magnetic waves. He probably felt he was better
acquainted with the waves through the medium of the General Equations,
and would 'not have known them any better, perhaps not so well,'
if he had met them in the laboratory. [7]

Yet even Maxwell had his blind spots. The electron as a basic,
quasi-atomic unit of electricity was clearly implied in his model of
ether-vortices, and in his theory of electrolysis. Yet he rejected the
concept of 'particles' of electricity as Faraday before had rejected
it. Thus, as already mentioned, it was left, to J. J. Thompson to take the
next decisive step: the identification of the electron as an elementary
unit of electricity, and at the same time an elementary particle of
matter. Some fifteen years later Rutherford discovered that the atom
had a positively charged nucleus; Moseley discovered that the number of
electrons in an atom determined its place in the periodic system; and Bohr
made his famous model of electrons circling round the nucleus like planets
round the sun. Matter and electricity had merged into a single matrix.
We have followed, though only in the scantest outline, the successive
confluences into a vast river-delta, of electricity, magnetism, light,
heat, and other electro-magnetic radiations; of chemistry, biochemistry,
and atomic physics. This development was, as we have seen
(
p. 228)
, accompanied by the realization that
the various 'powers of nature' were merely different forms of energy. In
earlier days, and well into the nineteenth century, each of these 'powers'
were thought to be contained in a material subsunce, a subtle fluid
or vapour or effluvium: heat in the phlogiston; organic energy in the
'vital fluid'; gravity in the ether; electricity and magnetism in their
separate effluvia. The word 'energy' from the Greek
energos
(work)
was for the first time used by Thomas Young in 1807 to designate kinetic
energy only. But by that time Rumford had already shown by an ingenious
experiment that mechanical energy could be converted into heat: he made
a blunt boring machine, driven by horses, work against a metal cylinder
underwater, and demonstrated that the heat thus produced actually brought
the water to the boil. By the middle of the century it became evident
that the powers of nature were convertible: mechanical motion into heat,
heat into motion, motion into electricity, electricity into magnetism,
and so forth. Thus one by one the various 'subtle fluids' dropped out of
the game, and were replaced by equations determining the exchange rates,
as it were, for the conversion of one kind of energy-currency into
another. Lastly, Einstein and his successors taught us that mass and
energy, particle and wave, are merely two aspects of one and the same
basic process. Only in one respect have they failed so far: in their
attempts to link the gravitational field and the electro-magnetic field
in a single system of equations, a unified field theory.

 

 

 

NOTES

 

 

To
p. 662
. The 'dip', or magnetic inclination
seems to have been discovered independently by Georg Hartmann, a
German clergyman, in 1544, and by Robert Norman, a compass-maker from
Wapping. Norman and Mercator also anticipated Gilbert by placing the
source of magnetic attraction in the earth.

 

 

To
p. 668
. The experiment was actually suggested
to Ampère by Arago.

 

 

To
p. 670
. Faraday's original formulation was
indeed entirely relativistic. According to Newtonian mechanics, however,
it did make a difference whether the wire was moved or the magnet. This
paradoxical asymmetry was one of the pincipal considerations which led
Einstein to the theory of special relativity (cf. Polànyi, 1957,
pp. 10-11).

 

 

To
p. 670
. Vortices had already appeared in
Kepler's and Descartes' explanations; and Helmholz, too, had compared
the dynamics of fluids with electric currents and magnetic fields;
but Maxwell's electro-hydro-dynamics were of an incomparably more
refined order.

 

 

To
p. 671
. Maxwell himself was less dogmatic about
it. 'For the sake of persons of different types of mind, scientific
truth should be presented in different forms and should be regarded
as equally scientific whether it appears in the robust form and vivid
colouting of a physical illustration or in the tenuity and paleness of
a symbolical expression.'

 

 

 

 

 

APPENDIX II:
SOME FEATURES OF GENIUS
1. THE SENSE OF WONDER
In one of his essays -- "The Cutting of an Agate" -- William Butler
Yeats voiced one of the silliest popular fallacies of our times:

Those learned men who are a terror to children and an ignominious sight
in lovers' eyes, all those butts of a traditional humour where there is
something of the wisdom of peasants, are mathematicians, theologians,
lawyers, men of science of various kinds.

The fallacy consists in the identification of 'men of science of various
kinds' with the lowest kind: the figure of the uninspired pedant in the
waxworks of popular imagination (