A RARE instrument discovered in a Falmouth basement back in the summer is set to hit the high seas as part of a history project.

In July members of the society were surprised to discover a magnetic dipping needle, built in Falmouth in 1845, in the bowels of Falmouth Art Gallery.

Still working, it was one of the most sophisticated instruments built in early Victorian Britain, to measure the Earth's magnetic field, Dr Edward Gillin, of the society, said.

He added: "It was also of the same exact type to pinpoint, for the first time, the Magnetic South Pole.

"Built in Cornwall, these devices were taken all over the world to make measurements."

Now, thanks to funding from the Tanner Trust, on January 6 Dr Gillin will be taking the needle to sea along the route of James Clark Ross' famous Antarctic Expedition of 1839-43, as far as Cape Town, via Cape Verde and St Helena.

During the voyage, magnetic experiments will be reenacted, with regular videos uploaded online and updates on Facebook and Twitter (@anderebus on Twitter and @dippingneedle1840).

It was in October 1839 that two ships passed off the coast of the Lizard, bound for the Antarctic.

Under the command of Captain James Clark Ross, the Royal Navy’s Terror and Erebus had been tasked with locating the magnetic South Pole and measuring the Earth’s magnetic field in the Southern Hemisphere.

To do this, both ships carried delicate magnetic instruments, known as dipping needles.

In the 1840s these were some of the most sophisticated devices in the world.

Those on board the Erebus and Terror had been designed by the Cornish natural philosopher, Robert Were Fox, and built in Falmouth.

Throughout the 1840s, almost every British naval expedition carried similar instruments for magnetic measurements.

A dipping needle is basically a magnetic compass, only instead of the needle sitting horizontally, it oscillates vertically, so as to measure the angle and intensity at which the Earth’s magnetic field is acting.

After a lobbying campaign under the leadership of Edward Sabine and John Herschel, the British government launched a huge surveying of the magnetic properties of the Earth in what became celebrated as the ‘Magnetic Crusade’.

Sending out ships to perform magnetic measurements and establishing observatories at Toronto, Tasmania, Cape Town, and St Helena, this was the largest state-funded scientific venture to date.

It was the world’s first truly global scientific survey and Falmouth was at the centre of the project.

Almost identical to those taken to the Southern Hemisphere in 1839, the Poly’s Fox-type needle was built in Falmouth and is the work of the instrument maker William George, a close associate of Fox’s.

Dr Gillin said: "Excitingly, and somewhat unbelievably, the needle itself is still magnetised.

"On returning to Falmouth in spring 2020, we will have experiments at Fox’s subtropical gardens of Penjerrick and RoseHill – his original testing sites for the needle due to their lack of magnetic interference.

"These will be public events and a rare chance to witness one of the most important productions of nineteenth-century Cornish science in action."