DESCRIPTIONS OF INSTRUMENTS. 



MAGNETOMETERS. 



Since the publication of Volumes I, II, and III, the Department of Terrestrial 

 Magnetism has not made any further material changes in the designs of magnet- 

 ometers heretofore used. The designations of the types of magnetometers used 

 for the work included in Volumes I, II, III, and IV are as follows: 



1. The so-called theodolite-magnetometer type in three designs, viz: (a) and (b) of the De- 

 partment of Terrestrial Magnetism, similar, respectively, to magnetometers Nos. 3 and 13, and 

 (c) of the United States Coast and Geodetic Survey, similar to C. & G. S. No. 20. 



2. The Kew type of magnetometer in two designs, with auxiliary theodolites for astronomical 

 work, viz: (a) the regular design as constructed by Elliott Brothers, similar to No. 73, and (6) 

 the Magnetic Survey of India design, similar to No. 36. 



3. The light and portable type used in the Magnetic Survey of France, similar to No. 11. 



4. The universal-magnetometer type in three designs, viz: (a) the design of Eschenhagen 

 and constructed with modifications by Tesdorpf, similar to No. 2025; (6) the magnetometer-dip- 

 circle design of the Department of Terrestrial Magnetism, similar to Nos. 14, 19, 20, 21, and 22; 

 (c) the magnetometer-inductor design of the same Department, similar to Nos. 23, 24, 25, 26, 

 27, and 28. 



The first three types, and design (a) of type 4, have been described and illustrated 

 in detail on pages 2 to 7 of Volume I, while designs (6) and (c) of type 4 have been de- 

 scribed and illustrated in detail on pages 5 to 12 of Volume II. Table 2 gives the details 

 and constants of the various magnetometers used in the present work. 



DIP CIRCLES AND EARTH INDUCTORS. 



The dip circles used in obtaining the data given in the present volume were of the 

 following patterns, of which the first two are fully described and illustrated in Volume I, 

 pages 7 to 10, and the last in Volume II, pages 7 to 12: (a) the regular Kew land-pattern 

 as made with slight variations by Dover and by Casella ; (6) the Lloyd-Creak ship-pattern 

 as originally designed by Captain Ettrick W. Creak and made by Dover with some 

 modifications introduced by the United States Coast and Geodetic Survey and by the 

 Department of Terrestrial Magnetism, according to L. A. Bauer's specifications; dip- 

 circle attachment of universal magnetometer of type 4 (b). 



The types of earth inductor used are fully described and illustrated in Volume I, 

 pages 10 to 11, and in Volume II, pages 13 to 15, and include: (a) the design originated 

 by Wild 1 and as modified by Eschenhagen represented in the Department's equipment 

 by No. 48 constructed by Schulze, and No. 2 constructed by Toepfer and Son; (b) earth 

 inductor of the type made by the Department of Terrestrial Magnetism for the deter- 

 mination of inclination at sea and as represented by earth inductors Nos. 3, 4, and 7; 

 earth-inductor attachment of universal magnetometer of type 4 (c) . 



A list of the various dip circles and earth inductors which were used, together with 

 the needles and their designations, will be found in Table 4, "Inclination Corrections on 

 Adopted International Magnetic Standard for the Period 1914-1920," pages 12 to 18. 



1 Wild, H. Inductions-Inclinatoriurn neuer Construction und Bestirnmung der Absoluten Inclination mit dem- 

 selben in Pawlowfik. St. Petersburg, Mem. Ac. Sc, eer. 7, vol. 38, No. 3, 1891. 



