By Michael Mosley

Presenter, The Story of Science

Please turn on JavaScript. Media requires JavaScript to play. Advertisement Scientific discoveries have shaped the development of society and civilisation throughout history, yet many of those with the greatest impact were accidental. NASA recently announced the discovery of five new exo-planets, planets that lie outside our solar system. They were found using NASA's Kepler space telescope, designed to find Earth-size planets orbiting sun-like stars. If there is alien life out there, it will probably be living on an exo-planet. I was particularly pleased to read about NASA's discovery because the man that telescope is named after - Johannes Kepler - is one of those wonderful characters who has contributed so much to our understanding of the universe, yet is something of an unsung hero. History shows that you can never know where a particular bit of research will take you or the questions it will raise

Son of a mercenary, Kepler was a 17th Century German astrologer and mathematician whose mother was tried as a witch. It was Kepler, and not Nicholas Copernicus, who first proved that the sun is the centre of the solar system and that the planets (including our own) travel round it in giant ellipses. It was Kepler's findings that helped lead to Newton's discovery of the laws of universal gravity, which changed our world. Paranormal FIND OUT MORE Michael Mosley presents The Story of Science Tuesdays, 9pm, BBC Two from 27 April

Watch clips from the series Yet like many of those who feature in my new series, The Story of Science, Kepler's discovery was an unexpected one, even to him. Having spent the last year looking into the history of science, one of the things that really stands out is its glorious unpredictability. History shows that you can never know where a particular bit of research will take you or the questions it will raise. Researchers who start off looking for one thing often end up discovering something quite unexpected. Like William Crookes, a 19th century British scientist with a passion for the paranormal. He claimed to have seen acts of levitation, an accordion playing by itself and strange phantom figures, some of which he photographed. He could be dismissed as a gullible fool, but the fact was that even in his own laboratory he was coming across things which were very hard to explain. Crookes thought it [radiation] was a fourth state of matter, one that was perhaps linked to the spirit world.

His most startling discoveries were made using fairly basic equipment: a partially evacuated glass tube, a couple of electrodes and a fluorescent screen. Crookes found that by passing a high voltage across the electrodes he could produce a green ray inside the tube. This ray could be bent with a magnet, suggesting it was in some way electrical. He then put a little paddle wheel into the tube and found that the green ray made it spin. Crookes called this "radiant matter" and thought it was a fourth state of matter, one that was perhaps linked to the spirit world. The physicist, Joseph John Thomson, came up with an equally outrageous, but ultimately more accurate, claim - that the green ray making the paddle wheel spin consisted of a stream of tiny charged particles, particles far smaller than atoms - the first sub-atomic particle to be discovered, later called electrons. First X-ray image And that was by no means all. In 1895, while experimenting with a Crookes tube, German physicist, Wilhelm Röntgen, discovered that as well as producing a green ray inside the tube, his equipment was also producing a mysterious ray that could be detected right across the room. Rontgen's picture of his wife's hand was one of the first X-ray images Not knowing what these rays were he called them "X-rays". One of the first pictures he took using these mysterious rays was of his wife's hand. When she saw it she apparently exclaimed "I have seen my death!" Hearing about Röntgen's work encouraged Frechman Henri Becquerel to investigate some unusual rocks he had in his collection, which glowed in the dark. His curiosity led to the discovery of radioactivity. An equally unlikely sequence of world changing discoveries came from attempts made in 1856 by an 18-year-old called William Perkin to find a treatment for one of the world's greatest killers, malaria. In his parents' converted attic in the East End of London, he set to work. But instead of a malaria cure he accidentally created an intense purple dye, which he called mauveine. It became all the rage and led to the discovery of other new colours, and an industry to produce them. Soon artificial dyes were being used not just to brighten clothes, but food and hair. In time they were used to stain cells, leading to the discovery of chromosomes and ultimately DNA. Dyes were the first chemicals to be made on a truly industrial scale and others, including fertilisers, soap and dynamite, quickly followed. Faraday demonstrates the invisible force of electro-magnetism The dye manufacturing process also produced large amounts of toxic chlorine gas, a gas which would later be used to terrifying effect in the First World War. The true value of blue-sky research is almost impossible to predict, which sometimes makes it hard to justify on purely commercial grounds. The story goes that Michael Faraday, the 19th century physicist who discovered the principles behind the electric generator and the electric motor, was asked by Gladstone, then Chancellor of the Exchequer, about the practical value of his discoveries. To which Faraday is said to have replied, "one day, sir, you may tax it". Michael Mosley presents The Story of Science on BBC Two on Tuesdays at 2100BST from 27 April. Watch more clips from the series.



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