I t is said that the astronomer William Herschel thought the surface of the sun was cool and solid, allowing peculiar beings to live there under a cloud layer that protected them from its heat. These creatures, he speculated, would have enormous heads, since a standard one might explode in such conditions.

Jim Bennett, director of Oxford’s Museum of the History of Science, cannot confirm that Herschel did actually believe this. Certainly though, like all great scientists, Herschel had an extraordinary imagination which enabled him to make huge practical advances in his field and many discoveries, including the existence of the planet Uranus. Herschel, who came from his native Germany to England, originally as a composer and organist, in 1757, is at the most recent end of the timespan covered by an exhibition at the museum, The English telescope from Newton to Herschel, the museum’s contribution to UNESCO’s International Year of astronomy in 2009.

The first patent application for a telescope, which was recorded in the Netherlands in 1608, and in 1609 the instrument came to the notice of Galileo, who set to work to improve it. The same year both he and an Englishman, Thomas Harriot, formerly a maths. student at Oxford (who mapped out the visible surface of the moon before Galileo) realised its potential for observing the night sky and began to use it to study the moon.

From the late 17th to the early 19th centuries, English telescope makers were responsible for technical developments which permitted not only greater academic investigation, but also the increasing popularity of astronomy as an amateur pastime — this was how Herschel came to embark on what turned out to be his life’s work.

The exhibits are drawn mainly from the museum’s own outstanding collection of instruments from this period, supplemented by many interesting documents and illustrations.

Two editions of Isaac Newton’s Opticks, from 1704 and 1721 introduce his designs for a reflecting telescope in which the image is created by a series of mirrors, instead of the sphere-section glass lenses previously employed in refracting telescopes, which failed to produce an even reasonably sharp image unless the tubes were extremely long. The maximum length recorded is 150 ft, on a telescope used in Danzig. Visitors can see some of the early English-made refractors, including a wooden instrument first owned by a Richard Owen of Aston, who is thought to have paid £50 for it in London. In an accompanying case are its object-glasses (lenses), one for daytime and one for the night.

A drawing by Robert Hooke, who also experimented with Newtonian designs, shows a 35ft refractor suspended from a pole in the courtyard of Gresham College, London. One case holds several small refracting telescopes, some with horn eyepieces and pasteboard tubes covered in white vellum with mottled gold, red or green inked decorations These had the object-glass in the smallest of the set of tubes, so that the instrument did not become difficult to handle as the tubes were pulled out.

Newton ground and polished his mirrors himself, as did many other astronomers. In 1738, Robert Smith, a professor of astronomy at Cambridge, published his own volume, also entitled Opticks, which can be seen in the exhibition and gives all the necessary directions for practical mirror-making, as well as the theoretical background.

Reflecting telescopes, particularly those developed by the mathematician James Gregory, which could be pointed directly at the object of interest, became the tools of a fashionable hobby for ladies, as well as gentlemen.

Herschel’s sister Caroline was a professional astronomer in her own right, responsible for many discoveries and for much of her brother’s record-keeping.

This newly possible exploration of the heavens was part of a growing popular interest in natural philosophy, and many people were quick to spot the commercial opportunities involved.

One enterprising chap, Charles Leadbetter, ‘Teacher of the Mathematicks’ at the Hand and Pen in Cock Lane, Shoreditch, produced for sale in London’s Optical Shops a helpful broadside print, giving “A Scheme of the true Appearances of the Satellites of Jupiter at Ten a Clock every Night in May, June and July Anno 1734; a Work entirely new and very useful for all those that makes Telescopic Observations”.

The exhibition includes a variety of Gregorian reflectors, including pocket telescopes in fish-skin cases, and brass models that could be screw-mounted on a travelling box. Nine of those on show were made by James Short, who moved from Edinburgh to London in 1738, and of whose instruments the museum has the most comprehensive collection anywhere.

Another telescope-manufacturer working in London during the middle decades of the 18th century was John Dollond, a silk-weaver of Huguenot ancestry. He specialised in refractors, having discovered that Newton’s rejection of the sphere-section glass lens had been based on an assumption that the uneven dispersion of light into its constituent colours — and the fuzzy image that this created — was the same for any sort of glass.

Dollond found that a combination of a high-lead glass and common optical glass could produce light that was bent without splitting into colours: he was made a Fellow of the Royal Society on the strength of his invention of the achromatic lens, and patented it in partnership with an instrument maker, Francis Watkins.

The exhibition goes, in some detail, into the rumpus that occurred after Dollond’s death, when his son Peter inherited half the patent and bought out the other share; having, however, to engage in extensive litigation to protect his father’s discovery.

Two documents are exhibited in which he defends John Dollond’s right to be regarded as the inventor of the achromatic lens.

The museum’s absorbing examination of this decisive period in the history of astronomy ends where we began, with the life of Herschel. His concept of enormous reflectors looking back through space and time to chart the evolution of the whole universe seemed mad to many of his fellow-scientists but which those of us living two hundred years later recognise as scientific reality.

Whether you are interested in the social history, the detailed physics of the optical instruments involved, or the astronomical discoveries they made possible, the exhibition will certainly give you pause for reflection.

n The exhibition runs until March 22, at the Museum of the History of Science, Broad Street, Oxford. Open Tuesday–Friday, noon-5pm, Saturday 10am-5pm, Sunday 2-5pm. A series of weekly lectures by distinguished astronomers runs throughout February, also children’s activities during half-term. There is an exhibition tour with Jim Bennett, and a family-friendly workshop, on March 21. Admission is free. 01865 277280