Physics was a relatively new subject of research in the nineteenth century.
As a result there was little funding, and many who wished to explore this
area had minimal facilities to do so.
However, around the end of the century, new university laboratories began to
open and many discoveries were made in the field of physics. The first such
university laboratory for physics teaching and research was set up in the
late nineteenth century following the pioneering work of Lord Kelvin in
Glasgow.
Subsequently the Cavendish Laboratory was opened in 1874 at Cambridge
University. This laboratory witnessed many new discoveries and nurtured some
of the most talented physicists. These included J.J. Thomson and Ernest
Rutherford.
Born in Manchester in 1856, Joseph John Thomson (known as 'J.J.') studied at
Owen's College (now Manchester University) and moved to Cambridge to study
mathematics. In 1884, aged 27, he became Cavendish Professor of Physics and
Head of the Cavendish Laboratory. The Laboratory had opened in 1874 under
James Clerk Maxwell, who was well known for his work on electricity and
magnetism.
J.J. Thomson’s most famous achievement was the discovery of the 'electron'
in 1897. Some scientists had already used the term electron to describe a
hypothetical unit of electricity. However J.J.’s breakthrough was proving
the existence of negative particles smaller than an atom. This was a profound
discovery at the time as some scientists were even sceptical of the existence
of atoms. This is not surprising since they are minute. A sheet of paper is
one million atoms thick. The famous scientist Rutherford described it by
explaining: 'If the entire population of the world were to spend their
working day doing nothing else, it would take them fifty years to count a
thimble full of atoms.'
The discovery of the electron showed that the atom has an internal structure.
J.J.’s experiment and subsequent theories won him the Nobel Prize for
physics in 1906, establishing him as one of the most influential scientists
of the twentieth century. A cathode tube used in his discovery of the
electron is on display in the Science Museum. In 1924 Thomson sent a postcard
explaining that he had been asked to display the apparatus used in his
experiment at the British Empire Exhibition in Wembley. Consequently, he
wished to borrow it from the Museum.
J.J. established a very successful research school at the Cavendish
Laboratory. Many of his students went on to be eminent physicists. Two
notable ones were Ernest Rutherford and a blood as well an academic
descendant, his own son G.P. Thomson.
Ernest Rutherford is one of the most famous scientists to have worked in
Britain. His most celebrated achievement was to ‘split the atom’, a concept
which caught the imagination of the public at the time of its development,
and continues to do so today.
Born in New Zealand, Rutherford came to England on a scholarship from the
Commission of the 1851 Great Exhibition. In 1895 he began work at the
Cavendish Laboratory at Cambridge University, under the guidance of J.J.
Thomson.
Rutherford’s first area of research was into radio waves, discovered a few
years before by Hertz. However with the encouragement of Thomson, Rutherford
turned his attentions to the newly discovered X-rays. It was during this
period that J.J. discovered the electron through his experiments on cathode
rays in 1897. How these electrons fitted into the atom was still unclear.
Thomson himself thought that they were embedded in a sphere of positive
charge, known as the ‘plum-pudding’ model.
However in 1913 Rutherford, along with the Danish physicist Niels Bohr,
dispelled J.J.’s theory and proved that an atom was made up of a positively
charged nucleus with electrons orbiting around it.
Initially Rutherford discovered the existence of a nucleus by considering the
work of Hans Geiger and Ernest Marsden, two colleagues at Manchester
University. They had bombarded gold foil with alpha particles. The results
were surprising. Rather than the particles being deflected, most went through
the foil, and a small number bounced back towards the source.
In 1911, Rutherford explained why this happened. He proposed that the atom
contained a nucleus in which most of the atom’s mass and positive charge
must be centred. This theory was then expanded by Bohr who believed that the
electrons, the negatively charged particles within the atom, rotated in
specific orbits around the nucleus. For example, a neutral hydrogen atom is
the simplest form of atom. It has a nucleus with a single positive charge and
one electron circling it. The model looks like a mini solar system.
So as Rutherford expanded these ideas at Manchester University, he completed
his most famous experiment – splitting the atom. He was the first to cause
an artificial break-up of an atomic nucleus as well as changing one element
into another. This he achieved by firing alpha-particles into an atom.
Occasionally one caused part of the nucleus to break off.
Rutherford then proposed that a positive charge in the nucleus was made up of
units, the basic unit being the nucleus of the hydrogen atom. He suggested
the term 'proton' for this unit.
Albert Einstein had already developed the idea of matter converting into
energy. Rutherford’s theory provided proof for this idea.
Though these discoveries were fundamental to the advancement of nuclear
physics, Rutherford was awarded with a Nobel Prize for Chemistry! This amused
him greatly as his work had been in atomic physics.
Advances in the understanding of the atom and its structure have given rise
to developments and theories in several areas of science. These include one
of the fundamental questions: how did the universe begin? One answer is the
Big Bang theory, which proposes that the universe emerged from nothing.
Immediately after the bang the new universe began expanding, filling up with
subatomic particles, including electrons.
George Paget Thomson was the son of J.J. Thomson and, like his father, was a
highly talented and brilliant man. After receiving a first class honours
degree in Mathematics and Physics, he went on to do research and teaching. He
aided the government in exploring the possible uses of fission for the war
effort. He was also interested in nuclear fusion, the process which makes the
sun shine.
Thomson’s most famous experiment was one that proved an earlier theory
developed by Lois de Broglie in 1924. This was that electrons had wave-like
properties.
During the middle of the 1920s he carried out a series of experiments using
an apparatus called an electron diffraction camera. This instrument is now on
display in the Science Museum. With it he bombarded very thin metal and
celluloid foils with a narrow electron beam. The beam was then scattered into
a series of rings.
Using these results, Thomson proved mathematically that the particles were
acting like waves. The process of electron diffraction, which his experiments
established, has been widely used in the investigation of the surfaces of
solids. This was a direct development of the work begun by his father with
the discovery of the electron.
For these achievements Thomson like his father before, won the Nobel Prize
for Physics, which he shared with C.J. Davisson in 1937.
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