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Prof. Francis Ring and Dr Rodney Hillier, on 5 September 2003
The Cambridge science historian, Dr Michael Hoskin, wrote scripts in the 1960s for a TV Series that was broadcast for A-level students. The series was called "The Mind of the Scientist." In each programme a modern scientist interviewed one from the past to find out how they succeeded in their mind-transforming discoveries. The historical characters were: Galileo, Newton, Herschel, Darwin and Pasteur.
The programme dealing with Herschel was entitled "The Depths of Space and Time". In this presentation, the part of Herschel was read by Prof. Ring dressed as William Herschel in his later years (early 19th century) with Dr Hillier reading the part of the modern scientist. The action was introduced by Herschel’s music – part of one of the symphonies recently recorded by the London Mozart Players – and at appropriate moments in the dialogue, diagrams and illustrations which would have appeared on the TV screen were projected.
Herschel briefly described his early life of music and how Ferguson’s book on astronomy inspired his interest. That book led him to believe that there were beings on all the heavenly bodies – even the Sun – but the Astronomer Royal had him cut references to rational beings from his first paper to the Royal Society on the height of lunar mountains. Smith’s ‘Optics’, which he read after reading the same author’s ‘Harmonics’, led him to make his first telescope.
He failed to measure the distance of the stars by parallax (measurements were not accurate enough to do this for another century). He admitted that his main fault was to ‘bite off more than he could chew’. As a first hypothesis he assumed that all the stars were like identical lamps so their apparent brightness was a measure of their distance. Every six months, when the Earth had moved nearly 200 million miles to the other side of the Sun, Herschel used a faint (therefore distant) star as a reference for measuring the movement of a nearby bright star. Though he failed to detect parallactic motion, he was the first to discover that some stars orbited others (binary stars), although this had been suggested before by John Michell.
In spite of realising that two such stars of very different brightnesses were at the same distance, he persisted in using the ‘faintness relates to distance’ idea when trying to determine how far the stars stretched – his quest for ‘the construction of the heavens’! When challenged on this he said that one had often to make improbable assumptions if one was going to get anywhere at all! He succeeded in establishing that the stars did not go on for ever by introducing the modern astronomical technique of ‘star-counts’. Thus he drew the first chart of our local star-system, ‘The Milky Way’.
The magnifying powers that Herschel claimed for his early telescopes were challenged but a trial showed that they were far better than anything at Greenwich Observatory. As a result he made hundreds of small telescopes, often for European royalty and nobility. He described some of the accidents he had and finally, his problems with the largest telescope in the world until 1848, the 40-foot reflector at Slough. He reasoned, by comparing the brightness of some of the stars he saw through it with that of the Sun, that their light must have been travelling millions of years. This was an extraordinary extension of Newton’s Universe, especially as at that time it was universally believed that Creation took place in 4004 BC.
When he started, only about 100 hazy luminous patches in the sky had been catalogued as ‘nebulae’, mainly by Messier. When Herschel had discovered some 2,500 more he classified them into types – he became a sort of heavenly naturalist. By doing this he hoped that he might determine how star systems changed with time. At first, he believed that they were all tiny conglomerations of stars which would, as some of them had, be resolved by larger and larger telescopes. He believed that he was seeing other star systems outside our own – an idea which was confirmed at the end of the 19th century. However, this theory fell apart when he discovered a nebula round a bright, and therefore close, star. He had to accept that some of his nebulae were indeed clouds of luminous gas.
When confronted with the debunking of his earlier theories he said "One must expect such things if one delves into great problems. During my life as an astronomer I have tried to maintain a proper balance between observation and theory. If you build a fanciful world of your own, without making observations, you can’t expect this to be the world of nature. On the other hand, if you simply pile up observations without drawing conclusions from them and without speculating about them, then you have wasted your time. And I have tried never to waste my time."
The modern astronomer justified Herschel’s dogged assumption that stars were like identically bright lamps in spite of his observations contradicting it, by noting that scientists are not enslaved by facts; hypotheses do not have to be rejected at the moment there’s trouble. He referred to a student of astrophysics who never made progress because, as soon as he had an idea he immediately saw reasons why it must be wrong – so he dropped the idea before he had given it a fair trial! Sir William has shown us how, in science, as in life, we sometimes have to live with contradictions.