Papers of the Board of Longitude : Correspondence on magnetic variation

Papers of the Board of Longitude

<p style='text-align: justify;'>A curiosity concerning magnetism and its relationship with electricity re-emerged in the conscious of the metropolitan scientific scene in the late eighteenth century with the development of the battery, which could manufacture electricity when required, thus making experimental work significantly easier. The work of Hans Christian Oersted and Michael Faraday [<a target='_blank' class='externalLink' href='http://collections.rmg.co.uk/collections/objects/127729.html'><img title="Link to RMG" alt='RMG icon' class='nmm_icon' src='/images/general/nmm_small.png'/></a>] followed at the start of the 1820s. The spike in interest in electricity and magnetism during this period lead to an increase in correspondence on this subject being sent to the Board of Longitude, enough to result in Astronomer Royal George Airy [<a target='_blank' class='externalLink' href='http://collections.rmg.co.uk/collections/objects/136564.html'><img title="Link to RMG" alt='RMG icon' class='nmm_icon' src='/images/general/nmm_small.png'/></a>] having to dedicate two volumes of papers from the Board of Longitude to correspondence on magnetic variation when he sorted the papers.</p><p style='text-align: justify;'>The increase in correspondence of this nature probably contributed to Michael Faraday being chosen to become one of three committee members when the Board of Longitude was transformed into a closed consultative committee for the Admiralty in 1828. It would be fair to suggest that those setting up the committee anticipated that a significant amount of future correspondence would be regarding magnetic instruments and therefore Faraday's knowledge of the subject would be essential to the functioning of the new committee.</p><p style='text-align: justify;'>There are several authors in this volume that submit schemes to the Board that are directly concerned with the finding longitude at sea using magnetic variation and its effect on compass needles, for example Lieutenant Milne wrote to Thomas Young (see <a target='_blank' class='externalLink' href='http://www.npg.org.uk/collections/search/portrait.php?mkey=mw41673'>portrait</a> in the National Portrait Gallery) in 1819 on more than one occasion believing that he had <a href='' onclick='store.loadPage(1);return false;'> “found out a new method of longitude, in consequence of discovering the causes of the variation of the compass, the local variation and the dip of the needle.” (RGO 14/43:334)</a> There is also the example of Mr N H Jaeger who <a href='' onclick='store.loadPage(1);return false;'> submitted a scheme (RGO 14/43:431)</a> for “finding the longitude by magnetic variation” which has been translated from the Norwegian in 1823. Another example is a <a href='' onclick='store.loadPage(1);return false;'> collection of letters (RGO 14/43:476a)</a> from a Mr W Cragg who addresses the Board on the issue of “the cause of the variation of the magnetic needle and the finding the longitude therefore” five times between 1825 and the start of 1828.</p><p style='text-align: justify;'>This volume also offers occasional insight into the reception of these schemes and inventions by Thomas Young, who was the first person after 1818, when he became Secretary to the Board, to read through the proposals fully and often advised on the way forward. For example there is a <a href='' onclick='store.loadPage(1);return false;'> note (RGO 14/43:447)</a> from Welbeck Street, Young's private residence, to John Barrow [<a target='_blank' class='externalLink' href='http://collections.rmg.co.uk/collections/objects/107723.html'><img title="Link to RMG" alt='RMG icon' class='nmm_icon' src='/images/general/nmm_small.png'/></a>] at the Admiralty regarding “Harvey's elaborate paper on magnetism” recommending that the content does not address the concerns of the Board of Longitude, yet a shorter version of the paper might be received by the Royal Society “with great gratitude” in 1823. We also see in a 1824 letter from Barrow to Young forwarding <a href='' onclick='store.loadPage(1);return false;'> the correspondence (RGO 14/43:396)</a> of T Johnstone on “the change of the variation of the compass and the discovery of the magnetic pole” that Young has <a href='' onclick='store.loadPage(1);return false;'> noted at the bottom “returned the letter” (RGO 14/43:395)</a> suggesting this was one way of dealing with those schemes judged to be impracticable.</p><p style='text-align: justify;'>Also significant in this volume is a <a href='/view/MS-RGO-00014-00011/1'> note (RGO 14/11:459)</a> to Thomas Young, from Edward Sabine [<a target='_blank' class='externalLink' href='http://collections.rmg.co.uk/collections/objects/107845.html'><img title="Link to RMG" alt='RMG icon' class='nmm_icon' src='/images/general/nmm_small.png'/></a>] on his calculations regarding the position of the magnetic pole and his plans to have Captain George Francis Lyon [<a target='_blank' class='externalLink' href='http://collections.rmg.co.uk/collections/objects/107600.html'><img title="Link to RMG" alt='RMG icon' class='nmm_icon' src='/images/general/nmm_small.png'/></a>] who is preparing to journey to the Southern Side of the Hudson's Strait where, if the Admiralty will supply him with a dipping needle [<a target='_blank' class='externalLink' href='http://collections.rmg.co.uk/collections/objects/42909.html'><img title="Link to RMG" alt='RMG icon' class='nmm_icon' src='/images/general/nmm_small.png'/></a>], he will conduct further experiments to confirm Sabine's theory. Sabine hopes that Young will mention it at the next Board of Longitude meeting which will cause the Admiralty to provide the instrument. This letter demonstrates the informal and nepotistic manner in which the Board's resources could sometimes be bestowed.</p><p style='text-align: justify;'>Towards the end of the volume there is an account of Peter Barlow's experiments on board the ships Leven, Conway and Griper [<a target='_blank' class='externalLink' href='http://collections.rmg.co.uk/collections/objects/6146.html'><img title="Link to RMG" alt='RMG icon' class='nmm_icon' src='/images/general/nmm_small.png'/></a>] for correcting the local attraction of the vessels. Peter Barlow was an English physicist who noticed that when a magnetic compass needle was suspended over a rotating iron disc the needle was deflected in the 1824, the same year that François Arago performed the same experiment with a copper disc. Barlow submits to the Board of Longitude from the Royal Military Academy at Woolwich a <a href='' onclick='store.loadPage(1);return false;'> letter (RGO 14/43:599)</a> with an “Explanation of a method of ascertaining by observation the local attraction of a ships guns etc. on the compass applicable in every position of the vessel and in every part of the world.” The correspondence contains over a dozen exchanges and the results of examinations of the theory on the ships. Both Young and the Admiralty's enthusiasm to take the proposal by Barlow further after it arrives in 1819 perhaps balances out Young's rather nepotistic interaction with Sabine, as Barlow was at the time he first wrote to John Barrow a man unknown to him or Thomas Young.</p><p style='text-align: justify;'>Finally again this volume illustrates the problem of communication by diagram or drawing; examples of particularly beautiful drawings that fail to convey the function of the machine or instrument being described can be found in the <a href='' onclick='store.loadPage(1);return false;'> proposal (RGO 14/43:442)</a> by Monsieur Somany and in the <a href='' onclick='store.loadPage(1);return false;'> marbled booklet (RGO 14/43:506)</a> containing Thomas Hope's theory on 'magnetic aura'.</p><p style='text-align: justify;'>Sophie Waring<br />History and Philosophy of Science<br />University of Cambridge<br /></p>