History may have to be rewritten according to a meteorologist who claims the most striking feature of a famous Constable painting – a rainbow – may have been added in afterwards.

Professor John Thornes from the University of Birmingham argued that the feature, seen in Salisbury Cathedral from the Meadows, was painted in to reflect the artist’s grief over his best friend’s death at a special talk laid on by the Salisbury Museum.

John Constable’s close friend John Fisher died on the afternoon of August 25, 1832 – but the original painting was first exhibited in 1831.

Professor Thornes’ findings explain how a re-assessment of the solar geometry of the painting, and Constable’s understanding of contemporary rainbow theory, suggest that the rainbow was added in at a later date as a homage to Mr Fisher.

The end of the rainbow can even be seen to rest on Mr Fisher’s house, where Constable stayed during his visits to Salisbury.

Mr Thornes said: “Constable was a great believer that painting is a science, something that should be pursued with the aim of understanding the laws of nature.

“This approach is clearly applied to the clouds and weather in his works, but it was not the case with all of his depictions of rainbows.

“Unlike clouds, rainbows are seen much less frequently in his work and were therefore often more mysterious in their symbolic function.”

The work, which has been displayed at the Tate, has been seen in Ipswich, Cardiff and St Davids. It is currently close to home at the Salisbury Museum.

Mr Thornes added: “Our understanding of the history of this work will now have to be rewritten. Of course, it’s very possible that there are number of other secrets that lie within the skies of his works and those of his contemporaries.”

Louise Tunnard from Salisbury Museum said staff were very interested to hear what Professor Thornes had to say.

She said: “It’s just astonishing when you think about how talented a scientist Constable must have been too to study the weather in such a way as to reflect the research at the time.

“Recently we have also had Anne Lyles who is a Constable expert in who backed up John’s theory by suggesting Constable was happier to use artistic licence in later life.

“For instance in this particular painting he exaggerated the cathedral and its spire to show its importance.”

More details about the research will be uploaded to Tate Britain’s Art Focus blog in the coming weeks.