1866.] Contributions to Terrestrial Magnetism, 209 



IV. "Contributions to Terrestrial Magnetism. — No.X.^^ By Lieut.- 

 General Edward Sabine, K.A., President of the Royal Society. 

 Received June 7, 1866. 



(Abstract.) 



In this number of the Contributions to Terrestrial Magnetism the author 

 resumes the discussion of the results obtained in the Magnetic Survey of 

 the Southern Ocean by the Expedition under Sir James Clark Ross, R.N., 

 and Captain Francis Rawdon Crozier, R.N., between the years 1839 and 

 1843. The proceedings during the two first years of this Survey have 

 been the subjects of two preceding numbers of the Contributions, viz. of 

 Nos. V. and VI., in the Philosophical Transactions for 1843 and 1844. 

 The present number contains a similarly detailed exposition of the 

 operations of the third year of the Survey, comprehending the Southern 

 Atlantic between Cape Hern and the Cape of Good Hope, and completing 

 the circumnavigation of the southern hemisphere, from the departure of 

 the expedition from the Cape of Good Hope in March 1840, to the return 

 to the same station in April 1843. In a subsequent memoir, which will 

 be presented to the Royal Society early in the ensuing Session, the author 

 proposes to connect and thoroughly coordinate the three portions of the 

 Survey, and to supply from them the numerical data at equidistant points 

 on each of the three parallels of 50°, 60°, and 70° of south latitude, of 

 the three magnetic elements, which will be required for a revision of the 

 ' Allgemeine Theorie des Erdmagnetismus' of M. Gauss — the 40th parallel 

 having been the most southern available at the epoch of the publication of 

 the original work. 



The instruments employed in this Survey, as well as the methods of 

 employing them, and of eliminating the disturbing influence of the iron in 

 the equipment of the vessels, having been in a great measure of a novel 

 character, a discussion of considerable length bearing on all such points is 

 prefixed to a full detail of the observations themselves, arranged in Tables, 

 showing in every instance both the immediate results of the observations, 

 and the corrections which have been applied in conformity with the prin- 

 ciples contained in the preliminary discussion. Tabular abstracts are also 

 furnished, exhibiting the results of the determinations of each day, with the 

 appropriate geographical positions. 



June 21, 1866. 



Lieut.-General SABINE, President, in the Chair. 



Dr. Hugo Miiller, Mr. Perkin, the Rev. Canon Selwyn, and the Rev. R. 

 Townsend, were admitted into the Society. 



