6<\/span> Volta\u2019s pile<\/h3>\n<\/div>\n\n
The prototype battery that its inventor perfected by giving himself electric shocks<\/strong><\/p>\nAlessandro 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 \u2013 current electricity.<\/p>\n
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 \u2013 the kind already observed in electric eels or twitching frogs\u2019 legs \u2013 was identical to artificial electricity produced in a laboratory.<\/p>\n
Volta was as interested in defeating his rivals \u2013 especially his fellow Italian Luigi Galvani \u2013 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.<\/p>\n
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7<\/span> Crookes tube<\/h3>\n<\/div>\n\n
The mysterious glowing apparatus in which electrons were discovered\u00a0<\/strong><\/em><\/p>\nIt\u2019s 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 \u2013 but what? \u2013 is strong enough to push a little cart along some miniature rails. Could it be a stream of particles, or perhaps some mysterious rays?<\/p>\n
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.<\/p>\n
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\u2019s evidence was persuasive, and he was partially vindicated when his rays were shown to be electrons. His s\u00e9ance experiences have never been fully explained.<\/p>\n
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8<\/span> Mrs Roentgen\u2019s ring<\/h3>\n<\/div>\n\n
The jewel in the crown of the world\u2019s first x-ray image<\/strong><\/p>\nAcademic articles rarely mention scientists\u2019 families, but this photograph suggests that 19th-century wives may often have been involved in research projects.<\/p>\n
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.<\/p>\n
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. \u201cI have seen my death\u201d she exclaimed prophetically when she was shown her bones with their ghostly coating of flesh. She was right \u2013 this weightless, electrically neutral radiation would often prove fatal. Yet within a few years, x-rays had entered the repertoire of fairground performers:<\/p>\n
\u201cI\u2019m full of daze; Shock and amaze;<\/em><\/p>\nFor now-a-days; I hear they\u2019ll gaze<\/em><\/p>\nThru\u2019 cloak and gown \u2013 and even stays; <\/em><\/p>\nThese naughty, naughty Roentgen Rays.\u201d<\/em><\/p>\n\u00a0<\/p>
9<\/span> Edwin Hubble\u2019s telescope<\/h3>\n<\/div>\n\n
The instrument that helped a First World War veteran establish that the universe is expanding<\/strong><\/p>\nNot 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 \u2013 his lab nickname was \u2018The Major\u2019 \u2013 Hubble went to the Mount Wilson observatory in California, where he used the world\u2019s largest telescope to discover nebulae lying far beyond our own galaxy.<\/p>\n
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.<\/p>\n
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 \u2013 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 \u2018big bang\u2019 was coined by one of the theory\u2019s most outspoken opponents.<\/p>\n
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10<\/span> Rosalind Franklin\u2019s x-ray photograph<\/h3>\n<\/div>\n\n
This image, taken in a London laboratory in the early 1950s, was crucial in unlocking the secrets of DNA<\/strong><\/p>\nWhen 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.<\/p>\n
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\u2019s instructions to get on with his own work, and instead engaged in clandestine meetings with Francis Crick as they struggled to solve science\u2019s biggest puzzle.<\/p>\n
When Watson was shown Franklin\u2019s picture without her knowledge, he immediately recognised its significance \u2013 \u201cmy mouth fell open and my pulse began to race,\u201d he reported in his bestselling book, The Double Helix<\/em>. 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.<\/p>\n\u00a0<\/p>\n
10\u00bd) \u2013 The hologram<\/h3>\n
The 3D image that made a 15-year journey from half-realised theory to practice<\/p>\n
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.<\/p>\n
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.<\/p>\n
Patricia Fara is the senior tutor of Clare College, Cambridge<\/strong><\/p>\nThis article was first published in the October 2011 issue of BBC History Magazine<\/a><\/em><\/strong><\/p><\/body><\/html>\n
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