1. Henry Cavendish (1731–1810)
As a fellow-scientist wrote, Henry Cavendish possessed a clarity of comprehension
and an acuteness of reasoning that have been the lot of very few
of his predecessors since the days of Newton. At home and abroad he was
regarded as the most distinguished British man of science of his day. Among
his many achievements are the demonstration of the existence of hydrogen
as a distinct substance, the demonstration that water is a compound and the
determination of the density of the earth. He was also one of the pioneers
of electrical research, presaging much of the work of Coulomb, Faraday and
Ohm. Clerk Maxwell, who edited some of his papers, was fascinated by
his character: ‘Cavendish cared more for investigation than publication. He
would undertake the most laborious researches in order to clear up a difficulty
which no-one but himself could appreciate, or was even aware of. And
we cannot doubt that the result of his enquiries, when successful, gave him
a certain degree of satisfaction. But it did not excite in him that desire to
communicate the discovery to others which, in the case of ordinary men of
science, generally ensures the publication of their results.’
Lord Charles Cavendish, the third son of the second Duke of
Devonshire, married Lady Anne Grey, the fourth daughter of Henry, Duke
of Kent. She was living in Nice, owing to frail health, when her first child Henry was born on
October 10, 1731. A second child, Frederick, was born
in England two years later, but their mother died shortly afterwards. Little
is known of the early years of the two boys, except that they attended
the Hackney Academy, a London school well thought of in its day for the
education of children of the upper classes in sound classical learning. Each
of the brothers went up to the University of Cambridge, matriculated as a
nobleman and resided there for four years, but left without taking a degree.
The college to which they belonged was St Peter’s, commonly known as
Peterhouse. Shortly after the younger brother had left Cambridge they made
the customary tour on the continent; apart from Paris, it is not known where
they went. Henry may well have studied mathematics and physics when he
was in Paris. The brothers did not have much to do with each other later in
life, although they remained on good terms.
After returning to England, Henry Cavendish went to live with his
father at a house in Great Marlborough Street, in the Soho district of London,
and apparently continued to do so until his father died. It was during this
period of almost thirty years that he carried out the fundamental electrical
research which so impressed Clerk Maxwell. He began his research career
by assisting his father, a gifted experimental physicist, who was a prominent
fellow of the Royal Society. Lord Charles made some valuable investigations
into heat, electricity and terrestrial magnetism. Franklin remarked that ‘It
were to be wished that this noble philosopher would communicate more of
his experiments to the world, as he makes many, and with great accuracy.’
Lord Charles was not a wealthy man but the financial allowance he
made to his eldest son was so small as to be described as niggardly by contemporaries.
It is not known just where the money came from, but, in 1783,

2. when his father died, or even before, Henry Cavendish became extremely
wealthy, apparently through a succession of legacies from relatives. However,
by this time he had become accustomed to living parsimoniously.
His large library of scientific works, housed in Bedford Square, was open
to any serious scholars. At one time it was in a somewhat neglected state,
so, having been told of a German scholar in straitened circumstances who
was capable of classifying the books in a satisfactory manner, Cavendish
arranged for him to act as his librarian; in return Cavendish gave him the
princely sum of £10 000, with which to purchase an annuity. He could be
remarkably generous when he felt so inclined.
Cavendish’s principal residence was a large villa at Clapham, then just
a village south of London. Most of its rooms were equipped with scientific
apparatus. It was at Clapham that he made his discovery of the composition of water and
measured by means of a torsion balance the density of the earth.
There was a ladder up a large tree in the garden, from the top of which he
made astronomical and meteorological observations. He was very much a
man of habit, invariably dining off leg of mutton and taking exactly the same
walk every day on his own. His pathologically shy and nervous disposition,
on which anyone who had any contact with Henry Cavendish was apt to
remark, has been attributed to his comparative poverty during the first forty
years of his life.
In appearance Cavendish was tall and thin, his face intelligent and
mild. His voice was hesitant and somewhat shrill. He retained the dress
of his youth – faded violet suit with high collar, frilled shirt-wrists and a
knocker-tailed periwig. Each year on a fixed day his tailor provided him with
a new suit that was a replica of the old one. When out-of-doors he was to
be seen wearing a three-cornered hat. He would often be accompanied by
Sir Charles Blagden, who for seven years acted as his assistant. As secretary
of the Royal Society, Blagden made frequent visits to the continent, usually
to Paris, where he was a friend of Berthollet and Laplace, amongst others, and
courted the lively widow of Antoine Lavoisier. When eventually Cavendish
parted with Blagden’s services he provided him with an annuity of £500 and
left him a legacy of £15 000 in his will.
Cavendish’s interests extended over a wide field of natural philosophy,
and every subject of investigation was subjected to a rigorous quantitative
examination. The results he obtained with simple methods and apparatus
were amazing. He was not only a highly skilled experimentalist but also
a capable mathematician. In common with others in England during this
period, he employed the methods of Newton, for example the fluxional
notation for differentiation. In chemistry he adhered to the old caloric
theory of heat, although the experiments he performed were helping to
undermine it. Like Newton, he had a deep dislike of controversy. As a result
he published remarkably little; for example only two research papers on
electricity, although, when Clerk Maxwell was editing Cavendish’s electrical
researches for publication, after his death, he found twenty packages full
of manuscripts on mathematical and experimental electricity.

3. The vast bulk of the Cavendish papers must have given Maxwell
pause, but, once he had begun, he found them fascinating. Cavendish had
quietly presaged many of the important results of the following century. He
had performed some extraordinarily accurate experiments with the crudest
of equipment, using a pair of pithballs, on strings, which repelled each other
to measure charge and his own body to measure resistance. In going through the papers Maxwell
found many of the experiments mentioned so original
that they seemed worth repeating, checking or improving. Cavendish
had done his experiments by making himself part of the electric circuit
and noticing how intense the electric shocks he felt under different circumstances
were. To check his conclusions he would summon his servant
Richard to replace him and then observe his servant’s reactions. Visitors
to his laboratory were often pressed into taking part instead of Richard;
Cavendish offended a visiting American physicist, who refused to act as a
guinea pig and went off saying ‘when an English man of science comes to
the United States we do not treat him like that’.
Although Franklin’s work had been published twenty years earlier,
Cavendish’s paper ‘An attempt to explain some of the principal phenomena
of electricity by means of an elastic fluid’ involves basically the same idea,
but gives it a mathematical treatment, quantitative rather than qualitative.
Both Cavendish and Franklin served on a committee of the Royal Society
to report on the best way of protecting buildings from lightning; they recommended
the installation of pointed conductors. However, others were in
favour of blunt ends, and George III agreed.Anotorious controversy erupted,
with political overtones, since pointed ends were thought somehow to be
unpatriotic.
Although Cavendish mainly lived as a recluse owing to a morbid
dislike of society, he nevertheless participated in the intellectual life of
London. He was a member of the Royal Society of Arts, a trustee of the
British Museum, a fellow of the Society of Antiquaries, a manager of the
Royal Institution and a foreign associate of the Paris Academy. Like his
father, he was prominent in the Royal Society, to which he was elected
in 1760, served on the Council and some of its committees; and regularly
attended the Dining Club, to which he often brought guests. They were
advised that it was useless to try to engage him in conversation on any
non-scientific topic. The only known portrait of him, now in the British
Museum, was drawn surreptitiously at one of the club dinners.
Henry, later Lord, Brougham recalled seeing him at a Royal Society
Conversazione and hearing ‘the shrill cry he uttered as he shuffled quickly
from room to room, seeming to be annoyed if looked at, but sometimes
approaching to hear what was passing among others. His walk was quick
and uneasy. He probably uttered fewer words in the course of his life than
any man who lived to fourscore years, not at all excepting the monks of La
Trappe.’ Of the many stories told about his idiosyncrasies, one concerns a
distinguished foreign scientist who said that he wished to meet ‘one of the greatest intellectual
ornaments of this country, and one of the most profound

4. philosophers of all time’. Cavendish was so embarrassed that he was
reduced to total silence and escaped in his carriage at the first opportunity.
Cavendish made a number of journeys by carriage within Britain,
always in the summer, when conditions of travel were least difficult, and
generally accompanied by Blagden. Although usually their main purpose
was to visit other men of science, generally some scientific work was done
en route; for example they studied the variation of barometric pressure with
altitude, or collected specimens of minerals to be examined at leisure on
their return. They inspected many of the places where science was being
applied in industry, as the industrial revolution began to gather momentum.
Often the people he met were later guests of his at the Royal Society Dining
Club.
Cavendish died on February 24, 1810, at the age of seventy-eight,
and was buried in All Saints Church, Derby, now designated the cathedral,
where his famous ancestor Bess of Hardwick had built an elaborate tomb
for herself. Owing to his frugal life-style, he had accumulated a fortune of
over a million pounds, a huge sum in those days; he was one of the richest
men in England. When he died none of this wealth went directly to support
scientific research; he believed that it should return to the family from
which it came. However, many years later the University of Cambridge benefited
from the generosity of the Cavendish family through the endowment
of the Cavendish Professorship of Experimental Physics and the Cavendish
Laboratory.
Charles Augustin Coulomb (1736–1806)
The end of the Thirty Years War left France the most powerful nation in
Europe. Although the golden age of French science was yet to come, some
remarkable physicists were already distinguishing themselves before the
end of the ancien r ´egime. One of the first was Coulomb, the subject of our
next profile. He has been described as the complete physicist, rivalled in
the eighteenth century only by Henry Cavendish, combining experimental
skill, accuracy of measurement and great originality with mathematical
powers adequate to all his demands. He invented the torsion balance and
used it to show that the force between electrically charged particles is proportional
to the product of their charges and inversely proportional to the
distance between them. This fundamental result is known as Coulomb’s
law; the unit of electrical charge is also named after him.