Guest post: An alternative longitude solution - Ralph Walker and magnetic variation

29 Feb 2012

Hannah Salisbury undertook a research internship at the National Maritime Museum in 2011 and has sent us this post based on her work, which revealed the story behind an unusual-looking compass now in the NMM collections: By the 1790s, after decades of development, finding longitude at sea by using timekeepers or the lunar distance method was finally beginning to seem a practical reality. Yet these methods still had their problems, and there was scope for alternative suggestions. In 1793 a man named Ralph Walker (1749-1824) appeared before the Board of Longitude with a compass of his own invention, which he promised would solve all of their longitude-based problems (and others besides). It was a grand claim for his instrument and method. This was Walker’s first foray into designing navigational instruments. The son of a Scottish farmer, Walker went to sea in 1768 aged 19, and quickly became master of the merchant vessels on which he was sailing, trading to the West Indies, the Baltic and America. In 1783 he settled as a planter in Jamaica with his Irish wife Jane; making use of slave labour, they most probably grew sugar or coffee. It was also in Jamaica that Walker built a prototype of his compass, mostly out of wood. The Governor of Jamaica was so impressed with the compass that he procured Walker a passage to London on the Providence under Captain William Bligh, to enable Walker to present his invention to the Admiralty and the Board of Longitude. Leaving Jane and their seven children behind, Walker arrived in London in August 1793. It would be six or seven years before he saw them again. To carry out Walker’s method for finding longitude, a mariner would use the sundial attachment on the compass to align the instrument to the true north-south plane. Comparing this reading with the direction in which the compass needle was pointing gave the magnetic variation. This could, in theory, be used to discover the longitude, by finding where supposed ‘magnetic meridians’ intersected with the observed latitude. Walker believed that his method was simpler than lunar distances, cheaper than chronometers, and deserving of a substantial reward from the Longitude Commisioners. Initial reactions may well have given Walker cause for hope. The results of trials were generally favourable; Admiral Macbride was so impressed with the compass that he ordered one to be made for his own use. However, the compass did not win glowing reviews all round. Nevil Maskelyne was particularly damning in his judgement, writing that the compass was neither particularly innovative nor useful. Reporting to the Board on 6 December 1794, Maskelyne criticised both the compass and the theory behind it. The compass relied on the sun to work; on a dull day, it would be useless, and even on too bright a day its functioning would be compromised. Problems were also likely to be caused by the presence of iron on board ships, and Maskelyne thought that Walker’s innovation of placing the compass needle on its side was likely to cause it to warp. Lastly, in the ‘present improved state of navigation’, Maskelyne did not consider that the idea of finding longitude through magnetic variation had anything to offer. Nevertheless, the Board did meet with Walker several times between 1793 and 1796, and sent his compass for repeated trials. Unfortunately for Walker, his longitude solution was indeed doomed to failure. He had oversimplified the laws of terrestrial magnetism, and in any case the presence of iron on ships would always be a problem for taking compass readings. Although the compass was not considered a viable longitude solution, it was seen as an improvement on other compasses then available, and this seems to be the light in which the Board saw it. Eventually, in June 1795, after repeated pleas for justice from Walker, the Board awarded him £200. The compasses proved popular with naval men, and were still in use in the 1850s. Nevertheless, only four are traceable today, one of which is held by the NMM. Although Walker would remain interested in the fate of his compasses, his main life’s work was actually as an engineer. He began this new career in 1795, his first work being the West India Docks – a quite remarkable achievement given that the docks were the largest construction of their kind in the world, and that Walker apparently had no engineering experience whatsoever. Over the remaining 27 years of his life, Walker worked on several other dock schemes, as well as harbour improvements, canals and the East London Water Works, and launched the career of his nephew James Walker (1781-1862), who went on to become one of the best-known civil engineers of his day. Walker was a clever and determined man, who took a great risk leaving his family in Jamaica while he took a chance on winning a longitude prize. Although he was not as successful in this as he had hoped, it led him to London and new work furthering Britain’s commercial and maritime interests through dock construction.