Tycho Brahe’s mural quadrant

The brass quarter-arc that helped an unorthodox Danish astronomer compile the world’s most accurate set of star data


Tycho Brahe was no ordinary 16th-century astronomer. Following an unfortunate duel he wore an artificial nose, and he supposedly died from a burst bladder at a feast.

More importantly, Tycho rejected conventional academic career routes, eventually acquiring royal funding for a massive observatory on the island of Hven, which is now a Danish heritage site on Swedish territory. He was particularly proud of his giant quadrant, the brass quarter-arc around two metres in height that curves across the frontispiece shown below.

Most of this picture is itself a picture – Tycho and his snoozing dog belong to a mural painted within the quadrant, which is fixed to the wall and used to measure the precise position of a star as it passes by the small sight on the top left. Behind the virtual Tycho’s outstretched arm lie illustrations of his observatory’s three floors: the roof top for making night-time observations, the library with its immense celestial globe, and the basement devoted to carrying out experiments. The real observer is just visible on the right, calling out to his assistants who co-ordinate their measurements of a moving star’s time and position.

Tycho compiled the world’s most accurate and comprehensive set of star data. And, although Tycho believed the Sun revolves about us, Galileo used his observations to confirm that the Earth indeed moves.


Johannes Kepler’s model of the universe

The harmonious musical cosmos imagined by the astronomer famous for showing that planets move in ellipses

In 1600, an impoverished astrologer and former university teacher called Johannes Kepler found refuge in the imperial court at Prague. His three laws describing how the planets move still lie at the heart of Newtonian astronomy, yet Kepler himself believed in a magnetic musical universe structured to mirror God’s perfect geometrical forms.

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In Kepler’s harmonious vision, which he illustrated by drawing an imaginary cosmic model, God had spaced out the planetary spheres so that symmetrical shapes could be nested between them. The outermost orbit of Saturn is separated from its neighbour – Jupiter – by a cube. Moving inwards, a pyramid lies between Jupiter and Mars. Similarly, other solids frame the paths of Earth, Venus and Mercury around the Sun.

Kepler decided that the Sun must affect the motion of the planets, and he started by tackling the astrological God of War, Mars. This planet’s orbit clearly deviated from circular perfection, and after many tortuous calculations and blind alleys,

Kepler showed that the orbit of Mars is an ellipse.

Yet what might now seem like a great scientific leap forward was ignored for decades. It was only in 1631, after Kepler had died, that his elliptical model was vindicated, when Mercury passed in front of the Sun exactly as he had predicted.


John Napier’s bones

The early calculator that made sums quick and easy

Have you ever wondered how the Romans did multiplication? Even the two-times table expands into nightmarish proportions if you try to work it out in Latin numerals. Hardly surprising, then, that when Hindu-Arabic numbers were imported into Europe at the beginning of the 13th century, merchants and mathematicians enthusiastically adopted the new system of nine digits plus zero that we still use.

Even so, when dealing with large numbers, it was easy to make mistakes. Division posed still more of a problem, to say nothing of square roots.

Four centuries later, the Laird of Merchistoun – better known as Scottish mathematician John Napier – decided it was time to make routine arithmetical tasks easier. He invented a special type of abacus, a set of rotating rods each inscribed many times over with the ten basic digits. Soon known as Napier’s bones (expensive ones were made of bone or ivory), this device made it possible to carry out long calculations quickly and accurately. You just line up the rods, and read off the answer.


Robert Boyle’s air pump

The device that produced a completely artificial state: a vacuum

Britain's most famous scientific picture by Joseph Wright of Derby (see top image), shows a red-robed philosopher lecturing about an air pump to a small family group, his hand poised on the stop-cock that will determine the life or death of a white bird inside the glass globe.

Developed a hundred years earlier by Robert Boyle and Robert Hooke, the air pump was a completely new type of instrument because it produced an artificial state – a vacuum. Boyle’s diagram below shows how, by turning the crank at the bottom, an experimenter could mechanically suck most of the air out of the glass globe. Critics may have denied that anything valid could be learnt about reality from a situation that was non-existent in nature, but the experiments were convincing. Moving bells inside the evacuated sphere could be seen but not heard, flames were extinguished, and rabbits died.

By the time that Wright was painting, the air pump had become an emblem of modern technology. His group portrait displays the mixed reactions still evoked by scientific research – wonder, absorption, terror – and also the complete lack of interest manifested by the couple on the left, who have eyes for nobody but each other.


Isaac Newton’s apple

The fruit that may or may not have fallen from a tree and inspired Newton’s theory of gravitation

Most people know only one thing about Isaac Newton: that he watched an apple fall from a tree. Rather like St Catherine’s wheel or St Jerome’s lion, Newton’s apple has become an iconic attribute of scientific genius.

The story originated with Newton himself, who as an elderly man reminisced about a day nearly 60 years earlier when “he sat in a contemplative mood. Why should that apple always descend perpendicularly to the ground, thought he to him self. Why should it not go sideways or upwards, but constantly to the earths centre? Assuredly, the reason is, that the earth draws it…”

For Newton and his contemporaries, this episode resonated symbolically with the Fall in the Garden of Eden, when Eve persuaded Adam to bite into the forbidden fruit from the tree of knowledge.

After a long absence, the apple reappeared in the 19th century and soon acquired mythological significance. When Oxford University built its Gothic-style museum for teaching science, stone statues were installed to inspire students. Newton was among the first six, gazing down at his apple as though it had fallen from heaven. We can never know whether that apple really did fall, but its impact has been enormous.


Volta’s pile

The prototype battery that its inventor perfected by giving himself electric shocks

Alessandro Volta was a sharp operator. Based in Italy, he consolidated his international reputation by cultivating scientific friendships all over Europe and pledging his allegiance to Napoleon. In 1800, he chose British journals for launching his revolutionary instrument that provided a new source of power – current electricity.

To make this prototype battery, Volta piled up discs on vertical glass rods, alternating two different metals and separating them with cardboard soaked in salty water. Incorporating himself as an experimental subject, Volta placed one hand in the basin of water at the bottom, and the other on the metal plate at the top. Sometimes he even used his tongue as a detector. The shocks he received were, he claimed, proof that animal electricity – the kind already observed in electric eels or twitching frogs’ legs – was identical to artificial electricity produced in a laboratory.

Volta was as interested in defeating his rivals – especially his fellow Italian Luigi Galvani – as in providing solid evidence. His article was a rhetorical masterpiece, convincing his readers by describing his results at length yet managing to avoid all the awkward questions.


Crookes tube

The mysterious glowing apparatus in which electrons were discovered

It’s the 1870s. Imagine the bewilderment of scientists gazing at this glowing electric tube. Inside, it contains only gas at a very low pressure, so what could be producing that eerie green luminosity? The strong shadow of a Maltese cross suggests that this is an optical phenomenon, but another experiment shows that something – but what? – is strong enough to push a little cart along some miniature rails. Could it be a stream of particles, or perhaps some mysterious rays?

This apparatus was developed by William Crookes, an ingenious British physicist who created movement and shadows to back up his claims that a strange substance is being emitted by one of the electric plates in his tube. Crookes suggested that spiritualism may be behind this, and after several prominent mediums survived his rigorous tests without being caught cheating, some eminent scientists believed that it really was possible to contact the dead.

Sceptics accused them of being duped by charlatans, but Crookes suggested that radio might have a human analogy, so that people with especially sensitive organs can tune in to vibrations carried through space. Crookes’s evidence was persuasive, and he was partially vindicated when his rays were shown to be electrons. His séance experiences have never been fully explained.


Mrs Roentgen’s ring

The jewel in the crown of the world’s first x-ray image

Academic articles rarely mention scientists’ families, but this photograph suggests that 19th-century wives may often have been involved in research projects.

When Wilhelm Roentgen stumbled across a mysterious type of radiation, he was a conscientious German professor methodically repeating some earlier experiments. While checking his apparatus to make sure it was light-proof, he noticed a strange shimmering some distance away. Roentgen then set about a systematic investigation, eating and sleeping in his laboratory for several weeks.

A fortnight after his initial discovery, he asked his wife, Anna Bertha, to hold her hand in the path of the rays that he labelled X to indicate his bafflement. “I have seen my death” she exclaimed prophetically when she was shown her bones with their ghostly coating of flesh. She was right – this weightless, electrically neutral radiation would often prove fatal. Yet within a few years, x-rays had entered the repertoire of fairground performers:

“I’m full of daze; Shock and amaze;

For now-a-days; I hear they’ll gaze

Thru’ cloak and gown – and even stays;

These naughty, naughty Roentgen Rays.”


Edwin Hubble’s telescope

The instrument that helped a First World War veteran establish that the universe is expanding

Not many people could make Albert Einstein admit he had made a mistake, but Edwin Hubble was one of them. After serving as a soldier in the First World War – his lab nickname was ‘The Major’ – Hubble went to the Mount Wilson observatory in California, where he used the world’s largest telescope to discover nebulae lying far beyond our own galaxy.

To measure the cosmos, Hubble needed an astronomical ruler, and he borrowed one invented by Henrietta Leavitt, a mathematical drudge or human computer based at Harvard. Like countless other intelligent women in this pre-electronic era, she was sufficiently desperate for work to tolerate long hours and low wages, and through tedious calculations she showed how flashing stars can be used to estimate stellar distances.

Thanks to Leavitt, Hubble produced his own graph proving that the further away a galaxy is, the faster it is racing away from the Earth. This diagram confirmed a consequence of relativity theory that Einstein had previously refused to accept – that the universe started out as a small dense cluster and has been expanding ever since. Although Einstein was converted, other scientists disagreed; ironically, the expression ‘big bang’ was coined by one of the theory’s most outspoken opponents.


Rosalind Franklin’s x-ray photograph

This image, taken in a London laboratory in the early 1950s, was crucial in unlocking the secrets of DNA

When the crystallographer Rosalind Franklin produced the x-ray photograph below, in London in the early 1950s, she carefully filed it away for future analysis. A firm believer in following scientific protocol, she had been trained to carry out her research methodically, and she was determined to complete her current set of experiments before exploring any further possibilities, however tantalising they might seem.

James Watson was a very different character. A young American PhD student at Cambridge, he was impulsive, ambitious and firmly focussed on his goal: to decipher the structure of DNA. Watson defied his boss’s instructions to get on with his own work, and instead engaged in clandestine meetings with Francis Crick as they struggled to solve science’s biggest puzzle.

When Watson was shown Franklin’s picture without her knowledge, he immediately recognised its significance – “my mouth fell open and my pulse began to race,” he reported in his bestselling book, The Double Helix. Although not an expert like Franklin, Watson knew that the prominent X shape revealed a spiral, and he realised later that two molecular strands must be intertwined. Fully analysing the photograph involved careful measurements and long calculations. Both Watson and Crick soon rushed into print, claiming that by unravelling the structure of complex molecules inside genes, they had discovered the secrets of inheritance. Franklin died young, in 1958, but her contribution to the understanding of DNA was already made.

10½) – The hologram

The 3D image that made a 15-year journey from half-realised theory to practice

Impossible to pin down with a photograph, holograms flicker from one half-state of existence to another. Unlike almost every other scientific invention, the theory underpinning holograms was thoroughly worked out long before the first one was created.

Dennis Gabor, a Hungarian Jew who had fled to Britain, developed the idea in 1947. Using standard laws of optical physics, he suggested that the 3D-appearance of an object might be recorded permanently, to be made visible once again by shining the same type of light as before. For years, holograms existed in a limbo state, envisaged intellectually but unrealised in practice. It was only after lasers were invented in 1960 that holography became feasible.

Patricia Fara is the senior tutor of Clare College, Cambridge


This article was first published in the October 2011 issue of BBC History Magazine