Reductions to Standard Instruments 



75 



CONSTANTS AND CORRECTIONS FOR LAND INSTRUMENTS. 

 Descriptions of Magnetometers and Dip Circles. 



The reduction formulse and methods of determining constants for the land instru- 

 ments, used in the Galilee shore-work and in the standardization of the ocean instruments 

 during 1905-1908, were the same as those in Volume I (pp. 22-41). 



The types of magnetometers used are described and illustrated in Volume I (pp. 2-7) ; 

 the details respecting them and the adopted constants for the period 1905-1908 are shown 

 in Table 21. 



Magnetometer 1 was manufactured by Fauth and Company, but, before assignment to 

 the Galilee, it was extensively overhauled and altered by the Department of Terrestrial 

 Magnetism; the magnets are hollow steel bars with cross-section of octagonal periphery 

 on the outside and circular on the inside, the long magnet being 7.2 cm. long, 0.7 cm. inside 

 diameter and 1.2 cm. outside diameter, and the short magnet being 6.0 cm. long, 0.7 cm. 

 inside diameter and 1 .2 cm. outside diameter. Magnetometers 3 and 4 were manufactured 

 by the Bausch and Lomb Optical Company of Rochester, New York; the magnets are 

 hollow cylinders, the long magnets being 7.5 cm. long, 0.75 cm. inside diameter and 1.00 cm. 

 outside diameter, and the short magnets being 3.5 cm. long, 0.61 cm. inside diameter and 

 0.82 cm. outside diameter. Magnetometers 30 and 36, loaned by the United States Coast 

 and Geodetic Survey, were manufactured by T. S. Cooke and Sons of London, England; 

 the magnets are hollow cyhnders, the long magnets being 9.27 cm. long, 0.76 cm. inside 

 diameter and 1.02 cm. outside diameter, and the short magnets being 4.33 cm. long, 0.62 

 cm. inside diameter and 0.83 cm. outside diameter. Phosphor-bronze-ribbon suspensions 

 were used for all the instruments except for magnetometer 1, in which the suspension was 

 of silk fiber. 



Table 21. — Details and Constants of Magnetometers Used, 1905-1908. 



[The c. o. s. system of units is used throughout this table; the value of a is given for 1® C] 



'This value of P is the value of P'. assuming that ( 1 + P'r'-) = (l+ Pr-^ + Qr *)■ 

 'Magnetometer 3 is the standard magnetometer of the Department of Terrestrial Magnetism. 



The dip circles used to determine the incUnation at shore stations were of the patterns 

 which are fully described and illustrated in Volume I (pp. 7-10), viz, (a) the regular Kew 

 land-pattern as made with shght variations by Dover and Casella, and (6) the Lloyd- 

 Creak ship-pattern, as originally designed by Captain Ettrick W. Creak and made by 

 Dover, and the modified type of (b), designated in the present volume as "sea dip-cu-cle" 

 (see p. 21 ) . To determine the magnetic dechnation at shore stations, a compass attachment, 

 fully described and illustrated in Volume I (p. 9), was provided for each land and sea dip- 

 circle. (See also the present volume, pp. 20, 22, and Plate 4, Fig. 1.) 



There was no earth inductor in the instrument equipment of the Galilee. Earth 

 inductor 48, constructed by Schulze, fully described and illustrated in Volume I (pp. 10-11), 

 was the standard inclination-instrument of the Department of Terrestrial Magnetism during 

 1905-1908. 



