6 



Land Magnetic Observations, 1911-13 



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. 



The magnet, stirrup, and suspension systems for all of the new instruments, listed 

 above under type 4 and made by the Department of Terrestrial Magnetism, are similar in 

 detail and dimensions to those for theodolite-magnetometers manufactured by the Depart- 

 ment of Terrestrial Magnetism of the type 1(6). These will be found described in detail 

 in the above reference to Volume I. Small differences, owing to slight mechanical altera- 

 tions, are sufficiently indicated in Table 1, which gives the details and constants of the 

 various magnetometers used in the present work. 



The suspension fiber for the new instruments is a phosphor-bronze ribbon ; for ordinary 

 work in the field this ribbon is of section 0.010 by 0.127 mm. For inertia determinations a 



Table 1. Details and Constants of Magnetometers Used, 1.91 1-1.913. 



[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 cyUnders, the long magnets being 7.5 cm. long, 0.75 cm. inside diameter and 1.00 cm. outside 

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

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

 13, 15, 16, and 17 (No. 18 of the same type is not yet completed) are of the theodolite-magnetometer tjTpe 1 (b) as 

 described in Volume I. Magnetometers 14, 19, 20, 21, and 22 are of the universal type, 4 (h), and are described on 

 pages 7-9 of the present volume (see PI. 2). Magnetometers Nos. 23 to 25 are of the combined magnetometer and 

 earth-inductor type which is described on pages 9-12 (see PI. 3). The magnets for Nos. 12 to 25 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 6.60 cm., outside diameter 0.79 cm.; short magnets, length 2.60 cm., inside diameter 0.45 cm., 

 outside diameter 0.65 cm. The suspension used for all the instruments referred to in the table is phosphor-bronze ribbon, 

 this material replacing the use of silk entirely in the field work of the Department. The deflection distances used for 

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



25, and 28 cm.) 



[The C.G.S. system of units is used throughout the t.iblc; the value of q is given for 1* C] 



'New scale added in July 1912. 



=These values given for F are the values of P', assuming that (1 + P'i--) = (l+Fr--+ (Jt-') ; this iniphes that the theoreti- 

 cal condition, (3 = 0, holds, since the dimensions of magnets were selected accordingly. 



'Constructed for Meterological Service of Canada. 



*.\fter extensive alterations and readjustments had been made. 



'The magnetometers here numbered 17, 19, 20, and 21 are not the same as those correspondingly numbered and 

 illustrated in Volume I, which are the property of the United States Coast and Geodetic Survey. 



'Constructed for the Magnetic Observatory of the Imperial University of Kazan, Russia. 



'Constructed for the Physical Laboratory of the Technological Institute, Tomsk, Siberia, Russia. 



