Observers' Field Reports 127 



E. N. Webb, on the Magnetic-Survey Results Obtained by the Australasian 



Antarctic Expedition, 1911-1913.' 



The instrumental outfit for the expedition included: a magnetograph, two 3-inch 

 theodolites by Negretti and Zambra provided with 4-inch trough needles, two 3-inch Gary 

 theodolites, chronometers, thermometers, hypsometer, aneroid, sledge-meter, and other 

 appurtenances. A Barrow dip circle was supphed by the Christchurch Ol^servatory, and 

 magnetometers Nos. 6 and 9, dip circles Nos. 169 and 178, and pocket chronometers Nos. 

 252 and 253 were supphed by the Department of Terrestrial Magnetism. 



Before leaving Hobart, in December 1911, the two sets of magnetic instruments were 

 carefullj- compared with the Department standards. (See Mr. Kidson's report, p. 109.) 

 At Macquarie Island, 2 primary stations were occupied, one at Caroline Cove, and the 

 other at the north end, where also 3 secondary declination stations were occupied. A land- 

 ing was next made at Commonwealth Bay, Adelie Land; here winter quarters were estab- 

 lished, and a magnetograph house and an absolute hut were constructed for the magnetic 

 work. During the 11 months at Commonwealth Bay, the magnetograph was in continuous 

 operation, except for about 15 days; absolute magnetic observations were made regularly 

 under very severe and trying circumstances.^ 



In an attempt to secure a magnetic station free from local disturbance, an ice cave 

 was excavated 250 feet above rock and one-half mile away from the rock outcrop. Two 

 complete sets of observations were secured here in the winter. 



During the autumn several attempts were made to carry out sledge journej^s, but, 

 owing to the exceedingly ^dolent winds, nothing was attained until finally in November 

 three parties were successfully started. Dr. Mawson with Lieut. Ninnis and Dr. Mertz 

 went east with two dog teams, carrying a light 3-inch Negretti and Zambra theodolite with 

 a trough needle. Messrs. Madigan and Correll and Dr. McLean went east also, carrying 

 a 3-meh Cary theodolite and the Christchurch dip circle. A third party, consisting of 

 Messrs. Bage, Webb, and Hurley, went south. 



Mr. Aladigan, on the eastern journey, observed both dip and declination at 6 stations, 

 declination only at 5 stations, and dip only at 2 stations, fairly evenly distributed over 270 

 miles. Several of these stations were on sea ice. 



The southern sledge journey, equipped with dip circle No. 178, Cary 3-inch theodohte, 

 hypsometer, etc., covered in all about 301 miles out by sledge-meter. Complete magnetic 

 observations were made at 7 stations evenly distributed, while rough determinations of 

 declination (with decUnometer and sun compass) were obtained at several camps. The dip 

 observed at the extreme station was 89 43'. 3 south. On the return journey the party 

 was hampered a great deal by continued overcast weather and falling snow, and was there- 

 fore unable to locate a depot 70 miles from base. With provisions almost exhausted, it 

 then became necessary to leave behind all outfit not absolutely necessary, and to make a 

 dash for the coast, arriving at headquarters considerably exhausted. Included in the outfit 

 thus abandoned was dip circle No. 178. The determinations of the total-intensity constant 

 and of the dip-needle corrections are therefore based entirely on intercomparison observa- 

 tions made before this journey, namely, at Hobart and Commonwealth Bay. 



'a fuller report will be published by the Australasian Antarctic Expedition. 



-The magnetic-observatory work will be discussed and published by the Australasian Antarctic Expedition. 



