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XX. Contributions to Terrestrial Magnetism. — No. X. 

 By Lieut.-General Edwabd Sabine, B.A., President of the Boyal Society. 



Received June 7, — Read June 14, 1866. 



I RESUME in this Number of the Contributions the discussion and coordination of the 

 observations of the Antarctic Magnetic Survey executed by Her Majesty's Ships ' Erebus' 

 and 'Terror,' under the direction of Sir James Clark Koss, R.N., aided by Captain 

 Francis Rawdon Crozier, RN., between the years 1839 and 1843. 



I purpose in the present communication to complete the detailed exposition of the 

 Survey by the reduction of the observations of the three magnetic elements in its con- 

 cluding year, on the same general plan on which similar accounts were given of those of 

 the preceding years in earlier communications, viz., between the Cape of Good Hope 

 and Hobarton in 1840, and between the departure from Hobarton in November 1840, 

 and the return to the same station in April 1841, in No. V. (Philosophical Transactions, 

 1843, Art. X.) ; and between Hobarton in July 1841 and the Falkland Islands in April 

 1842 in No. VI. (Philosophical Transactions, 1844, Art. VII.). The observations discussed 

 in the present memoir are those made from the departure from the Fa,lkland islands in 

 September 1842 to the second arrival at the Cape of Good Hope in April 1843. In a 

 subsequent and concluding memoir, which I hope to present to the Society early in the 

 ensuing session, it will be my endeavour to connect and thoroughly coordinate the 

 several portions of the Survey, comprising in its three portions the circumnavigation of 

 the Southern Ocean from the departure from the Cape of Good Hope in March 1840, 

 to the return of the ships to the same station in April 1843. 



The great work of M. Gauss, the ' AUgemeine Theorie des Erdmagnetismus,' had 

 been published in the 'Resultate des magnetischen Vereins' in 1839*. No more con- 

 clusive evidence could have been produced than was presented by that work, in support 

 of the representations which had been made to Her Majesty's Government conjointly 

 by the Eoyal Socie;ty and the British Association for the Advancement of Science, of the 

 advisability of a southern magnetic Survey. The requisite numerical values, on which the 

 practical application of the " AUgemeine Theorie" depended as a representation of the 

 magnetic phenomena oi the globe, and which were taken at equidistant meridional 

 points on parallels of latitude, were necessarily Hmited, by the imperfection of our then 

 knowledge, to seven such parallels, the most southern of which was the parallel of 40° 

 south. The investigations and conclusions resulting from the Survey now under consi- 

 deration, aided by the supplementary voyage of Her Majesty's Ship ' Pagoda,' under 

 • An English translation of this work was published in 1840 in the Vl.th Part of Tatiob's Scientific Memoirs. 

 MDCCCLXVI. 3 S 



