Descriptions of Instruments 



Table 2. Details and Constants of Magnetometers Used, 1914-1920. 



[Magnetometers Nos. 2 to 10 inclusive were manufactured by the Bausch and Lomb Optical Company of Rochester, New 

 York, and are all, except for minor mechanical details, of the same type, namely, 1(a), as described in Volume I; the 

 magnets are hollow cylinders, the long magnets being 7.5 cm. long, 0.75 cm. inside diameter and 1.00 cm. outside diam- 

 eter; the short magnets are 3.50 cm. long, 0.60 cm. inside diameter and 0.82 cm. outside diameter. Magnetometers 

 Nos. 12 to 25 were manufactured in the instrument shop of the Department of Terrestrial Magnetism. Nos. 12, 13, 15, 

 16, 17, and 18 are of the theodolite-magnetometer type 1(6) as described in Volume I. Magnetometers 14, 19, 20, 21, 

 and 22 are of the universal type 4(6) and magnetometers Nos. 23 to 28 are of the combined magnetometer and earth- 

 inductor type 4(c), as described in Volume II. The magnets for Nos. 12 to 28 inclusive are all of the same type, 

 being hollow cylinders made as nearly perfect as mechanically possible, the long magnets having the length 5.60 cm., 

 inside diameter 0.60 cm., outside diameter 0.79 cm.; short magnets, length 2.60 cm., inside diameter 0.45 cm., out- 

 side diameter 0.65 cm. The suspension used for all the instruments is phosphor-bronze ribbon, this material replacing 

 the use of silk entirely in the field work of the Department. The deflection distances provided for magnetometers 

 Nos. 2 to 10 inclusive are 25, 27.5, 30, 35, and 40 cm, and for magnetometers 12 to 28 inclusive, 20, 25, and 28 cm.] 

 [The C. G. S. system of unite is used throughout the table; the value of q is given for 1C] 



'When no values are entered for Q the values given for P are the values of P', assuming that (1 + P i-) = (1 + Pr* 

 + <2r-) ; this implies that the theoretical condition, = 0, holds, since the dimensions of magnets were selected accordingly. 



'Value given in Table 1, page 6, of Volume II is a misprint and should read 664 instead of 624. 



Instrument was remade in April 1918 and specially adapted for the field work in the Arctic of the "Maud Expedition" 

 of Captain Roald Amundsen. 



'Instrument was overhauled and repaired during July 1915 and Aug. 1916; it was not used in the field during the 

 interim. 



Instrument was remade during Nov. 1916 to Feb. 1917. 



Instrument was reconstructed during April to May 1918 



' Instrument was damaged by an accident on July 24, 1914, in the field; it was remade during June to July 1915. 



* Instrument was damaged by an accident on Oct. 5, 1914, in the field; it was remade during Feb. to April 1915 for the 

 Dominion Astronomical Observatory, Ottawa, Canada. 



' Instrument was overhauled and repaired during Aug. 1916. 

 ' Instrument was overhauled and repaired during July 1919. 

 " Constructed for the Moscow University, Moscow, Russia. 



" Manufactured by C. L. Berger and Sons for University of Texas, Austin, Texas; similar to theodolite-magnetometer 

 of type 1(6) as constructed by Department of Terrestrial Magnetism. Deflection distances used were 22 and 25 cm. 



