Mrs Pam Arnold-Palmer, a direct descendent of Nevil Maskelyne (1732-1811), recently donated to the Museum a fascinating collection associated with the fifth Astronomer Royal, who worked at the Royal Observatory, Greenwich from 1765 until his death in 1811. The objects range from letters to medals, notebooks to clothing, chronometers to sketches. Maskelyne is principally known for creating the first Nautical Almanac, published in 1766, which provided the tables seamen needed to enable them to find longitude from sextant measurements of the Sun, Moon and stars. The medals show how widely his work was appreciated as they include examples from Russia, France and USA, as well as the Copley gold medal of the Royal Society of London. Maskelyne’s international links are also highlighted by his correspondence with astronomers in other parts of Europe.

The letters, notebooks and accounts contain much interesting material about Maskelyne’s role in preparing the scientific work of several voyages of exploration. They reveal the equipment he recommended and some of his efforts to secure the services of suitable astronomers to carry out observations. These documents are a fascinating combination of the official and the personal, throwing light on his life at Greenwich and his recipes for various medicinal remedies, as well as his work as Astronomer Royal. The clothing includes dresses belonging to his wife, Sophia, and only daughter, Margaret, as well as a padded silk observing suit sent from India by his brother-in-law, Robert Clive.  The personal nature of much of this material helps to provide a more rounded picture of Maskelyne than emerges from the official records of the Observatory, or from more recent accounts of the story of finding a method of measuring longitude at sea.

‘Portrait of Nevil Maskelyne by John Russell RA, made when Maskelyne was in his forties’ (ZBA4305)

People often ask why the Greenwich Meridian is where it is and which came first, the line or the Observatory. The short answer is that the Observatory came first and the line is where it is because of the Observatory. But it’s a bit more complicated than that!

The Greenwich Meridian

A meridian is any imaginary line running from the North Pole to the South Pole. Astronomers who wanted to plot the positions of stars and planets set their telescopes up on a meridian, which they used as a reference line for their measurements and charts.

In 1850 the Astronomer Royal at that time, George Airy, ordered a new and much more accurate telescope, which he designed himself. It was much larger than previous telescopes so he had to find firms who were capable of making it.

The seventh Astronomer Royal, George Biddell Airy

For the metal castings he chose the engineers Ransomes and Sims of Ipswich. They specialised in agricultural machinery, but had some of the best manufacturing facilities in the country and were related to Airy through his mother. The lenses and other optical parts were made by a well-known firm of specialist opticians in London, Troughton and Simms. They had made other telescopes for the Observatory, so Airy was confident of their ability.

Airy’s transit circle, completed in 1851

The new design was for a type of telescope called a transit circle. The name comes from the fact that it was fixed on a north-south line for the observation of stars as they crossed, or transited, the meridian. It also had a circular scale for measuring the height of the stars above the horizon. The line through the centre of this telescope became the Greenwich Meridian.