Watercolour painting showing Airy’s ‘Magnet House’. It is thought to be the work of Richarda Airy or Elizabeth Smith and is dated on the back.

In 1816, the Admiralty ordered the Astronomer Royal, John Pond, to make regular observations of magnetic variation (declination). Pond’s ‘Magnetic House’, built in the Lower Garden, proved to have unstable foundations and was demolished in 1824, at which point observations ceased. Pond’s successor, George Airy, recognised the importance of magnetic work and persuaded the Admiralty to fund the establishment and staffing of a new Magnetic Observatory. Further grounds in the park were secured and an extension to the south fenced off in 1837.

Airy’s Magnetic Observatory was completed in May 1838. The building, which stood where the Peter Harrison Planetarium now stands, was cruciform in shape. It was built of wood on a concrete foundation, materials such as iron and brick being excluded to avoid their risk of residual magnetism.

In this painting of the Magnet House, the person on the bottom right quarter of the image is checking the Ground Thermometers. The cubical hut to his right was used to house a dip circle, most likely the dip circle now held in the National Maritime Museum [http://collections.rmg.co.uk/collections/objects/10922.html]. The little structure to the left of the figure in the centre of the image possibly housed two rain gauges (pluviometers). The large pole in the image is the electrometer mast, which stood 80 feet high.

For further views of the Magnetic Observatory, see [RGO 116/3/3], [RGO 116/3/9], [RGO 116/3/11], [RGO 116/5/6] and [RGO 116/5/9].