Welcome back to the origins of the aether. In this part, we will examine how the science of
electricity was taken from simple static charge to examine the flow of charge.
Until the last decade of the 18th century, most scientists who studied
the phenomena of electricity were only really looking at static electricity.
In 1752 Johan Sulzer had mentioned that a sandwich of silver and lead when joined
together and placed on the tongue gives the taste of the vitriol of iron. Yet neither of
the metals alone gives any trance of this taste. He postulated that the combination of the two
sets up a vibration in their particles, which by affecting the nerves of the tongue, produce the
taste in question. At the time his observations had no direct connection with electricity.
In 1780 Luigi Galvani was studying the susceptibility of the nerves to irritation.
During a dissection of a frog, a piece of electrical equipment nearby
happened to accidentally touch a nerve in the frog causing the muscle to convulse.
Further experiments revealed that the convulsions were caused by the transport of a peculiar fluid
from the nerves to the muscles. Galvani considered this fluid to be the same as the
ordinary electric fluid and regarded this process to be similar to the discharge from a Leyden jar.
Galvani’s idea would cause much outrage and quickly three different camps formed. One
who believed in Galvani’s ideas, those that felt the two fluids were of a different type
and lastly a group who refused to attribute the effects to a supposed fluid in the nervous system.
Alessandro Volta was firmly in the latter camp.
In 1792 he put forward the view that the stimulus in Galvani’s experiment is derived essentially
from the connection of two different metals by a moist body.
In 1796 Giovanni Fabbroni had observed that when two plates of different metals were placed in
water one of them would be partially oxidised when they were put into contact. From this,
he rightly concluded that some chemical action was inseparably connected with the galvanic effect.
At this stage, the galvanic effect was very weak in comparison with electrostatic experiments.
One year after Galvani’s death in 1800 Volta would make a breakthrough that would change this.
He had discovered a means of greatly increasing the intensity of the effect.
His breakthrough was to create a series of couples of zinc and copper disks which were
separated by a thin disk of moist plasterboard. It now resembled a Leyden Jar in terms of power
but had the ability to automatically re-establishing its state after each discharge.
Volta thought that the combination of the two metals set up a tension,
allow the copper to become negative and the zinc positive.
This idea seems to be a mingling of the two ideas of electric charge and electric potential.
At the time it was known that electricity was capable of inducing chemical action.
A solution of metallic salts would be decomposed by the current
but exactly how and why this occurred was fiercely debated.
It was Jons Jacob Berzelius who would take the next step forward. He put forward a theory that
explained that the chemical affinity arises from the play of electric forces, which in turn spring
from electric charges within the atoms of matter. To be precise, he supposed each atom possessed
two poles, which are the seat of opposite electricfications, and whose electrostatic
field is the cause of chemical affinity. Two atoms which are about to unite, dispose themselves so
that the positive pole of one touches the negative pole of the other; electricities
of these two poles then discharge each other, giving rise to the heat and light which are
observed to accompany the act of combination. The result leaves the compound molecule. This
action can then be undone through electrolysis which is able to separate the two atoms again.
This simple concept would later be overthrown by Faraday.
Most of his ideas would not even survive during his lifetime but the most important
that did survive was the idea that chemical affinities are of an electric origin.
Interest had begun to grow into the phenomena whereby steel could become magnetised by a
lightning strike. Hans Christian Oersted was the first to conduct experiments to examine
the effect of electricity on a magnetised needle. He was able to demonstrate that a magnetised need
would be deflected by a wire running parallel to the needle.
This led to the discovery that magnetic fields
could be produced by electric currents as well as magnets.
Andre Marie Ampere exactly a week after Oersted’s discovery was able to show that two parallel wires
carrying current would attract each other if the currents were in the same direction.
Ampere continued to study the phenomena and in 1825 published his collected results
in one of the most celebrated memoirs.
Ampere firmly believed in the concept of equal and oppositely directed forces
between pairs of particles and he rejected the idea of seeking a more speculative explanation
in terms of fluids or aethers. Nevertheless,
he indicated two conceptions which are related to an aether concept.
In the first, he suggested that the ponderomotive force between
circuits carrying electric currents may be due to the reaction of the elastic fluid
which extends throughout all space, whose vibrations produce the phenomena of light
and which is put in motion by electric currents. This fluid or aether he said
could be no other than that which results from the combination of the two electricities.
In the second conception, he suggests that the interspaces between metallic molecules of a wire
which carries a current may be occupied by a fluid composed of the two electricities,
not in the proportions which form the neutral fluid, but with an
excess of one type and which consequently masks the other.
Ampere developed the theory of the equivalence of magnets with circuits carrying currents.
He showed that an electric current is equivalent, in its magnetic effects,
to a distribution of magnetism on any surface terminated by the circuit.
He preferred to consider the current rather than the magnetic fluid as the fundamental entity.
To him, magnetism was really an electrical phenomenon.
Each magnetic molecule owes its properties, according to this view, to the presence within
it of a smaller closed circuit in which an electric current is perpetually flowing.
So impressive was Ampere’s work that it would leave a lasting mark.
Almost 50 years later Maxwell would refer to it as one of the most brilliant achievements in science.
Not long after the discoveries of Oersted a connection was discovered between galvanism
and heat. In 1822 Thomas Johann Seebeck announced that an electric current can be
set up in a circuit of metals merely by having a temperature gradient. To
this new class of circuits, the name thermo-electric was given.
Cavendish had investigated the power of metals to conduct
electrostatic discharges. Davy took this further by examining the conducting voltaic currents.
He discovered that the conducting power of a wire formed from any metal is inversely
proportional to its length and directly proportional to its cross-sectional area,
but independent of the shape of the cross-section. This showed that voltaic currents flowed through
the substance of the conductor and not along its surface. He also studied the effect of temperature
and found that the conductivity varied with temperature. Being lower at higher temperatures.
He also observed that the same magnetic power is exhibited by every part of the same circuit,
even though it is formed of wires of different conducting powers pieced into a chain.
The current which flows in a voltaic circuit, therefore, depended not only
on the conductors which form the circuit, but also the driving power of the battery.
In order to form a complete theory of voltaic circuits, it was, therefore, necessary to extend
Davy’s laws by taking this into account. This advancement would come in 1826 by Georg Simon Ohm.
Ohm had already carried out a considerable amount of experimental work on the subject.
His focus was on combining all the known results into a consistent theory.
For this purpose, he adopted the idea of comparing the flow of electricity in a current
to the flow of heat along a wire. This would allow the electricity to be passed on from one
particle to the next only if they were situated close enough to each other. This comparison led
directly to the adoption of a driving power acting on the electricity. In order to achieve this,
he had to rely on Volta’s theory of the electrostatic condition of the open pile.
Ohm’s memoirs marked a great advance in electrical philosophy. It was now clearly understood that the
current flowing in any conductor depends only on the conductivity inherent in the conductor and on
another variable which bears to electricity the same relation to that temperature bears to heat.
This was the key to connecting the theory of current with the older theories of electrostatics.
In the next part, we will return to looking at the developments of the aether concepts.