8 Land Magnetic Observations, 1914-20 



INSTRUMENTS FOR THE AMUNDSEN ARCTIC EXPEDITION. 



As the result of a conference in April 1918 between Captain Roald Amundsen, Dr. 

 Fridtjof Nansen, and the Director, certain minor modifications were decided upon in the 

 C. I. W. instruments to be supplied by the Department for the magnetic observations 

 it was proposed to undertake on the Amundsen Arctic Expedition (the "Maud Expe- 

 dition"). These modifications, none of which altered the intrinsic design of the instru- 

 ments, were based upon the following considerations resulting particularly from the 

 Arctic experiences of Dr. Nansen, Captain Amundsen, and Mr. Peters of the De- 

 partment : 



(a) Difficulties arising from extreme cold, condensation that occurs from lamps and the 

 proximity of the uncovered hands as well as the breath, and the lack of delicate touch and the 

 necessity of wearing mits; these difficulties, of course, apply chiefly to the work in winter. 



(6) Any one instrument should have the least possible number of parts to be assembled, 

 thus permitting rapid unpacking and assembling, and dismounting and repacking. 



(c) All clamping screws, tangent screws, and other metal parts of the instrument which 

 must be touched with bare fingers during adjustment, or observation, should be suitably covered 

 with non-conducting materials; such covers should also be made of sufficient size to facilitate 

 delicate clamping and adjustment with numbed fingers. 



(d) All glass lying between the observer's eye, and the graduation, scale, or object that he 

 must read or observe, should be readily accessible for removal of condensation. (For obser- 

 vations in extreme cold it is necessary to refrain, as much as possible, from breathing on the 

 instrument.) 



The C. I. W. magnetometer No. 8 of the Department's type 1 (a) and Dover dip- 

 circle No. 205 were selected as instruments most nearly answering the requirements 

 specified by Captain Amundsen. They were modified and altered by providing all parts 

 subject to handling in use and adjustment in the field with celluloid covers. The hood 

 connection between the magnetometer-telescope and its house was altered so as to elim- 

 inate the necessity of fitting the hood to the telescope when assembling the instrument. 

 This was accomplished by the addition of a spherical-ended cap on the objective end of 

 the telescope, arranged to make contact with a velvet-lined, concave mounting attached 

 to the magnetometer-house (this arrangement is similar to that used on the later types 

 of C. I. W. magnetometers). Celluloid grips were also mounted on the reversing bar- 

 magnets of the dip circle. The arresting device for the compass attachment of the dip- 

 circle was altered by an eccentric mechanism to facilitate clamping and unclamping of 

 the needle. A special lifting device was made by which the dip needles could be lifted off 

 the agate supports and turned face about without opening the magnet-house; however, 

 as its operation seemed to involve some danger of accident to the needles, this attachment 

 was removed from the instrument before it was sent away. A more detailed idea of the 

 modifications which were made may be obtained by an inspection of Plate 2 which shows 

 various views of the magnetometer and dip circle. 



