12 Land Magnetic Observations, 1911-13 



the suspension and removing torsion of the fiber. The entire length of the suspension 

 from the point of attachment to the magnet system is about 120 mm. A special clamp 

 has been provided for clamping the magnet system in place when the instrument is being 

 transported or when not in use. This is shown in Plate 3, Fig. 4; it consists of one fixed 

 arm with a V-cut surface to receive the brass wire of the suspension, and a second mo\'able 

 arm with corresponding V-surface at its end, held in place by a spring operated through 

 a milled nut on the outside of the instrument, ^\^len this nut is loosened the spring forces 

 the movable arm against the fixed arm, clamping the suspension. The clamping surfaces 

 in contact are sufficiently long to insure no deformation of the suspension system. 



A piano-parallel glass window has been provided in the damping-box on one side 

 of the instrument, so that readings may be made by means of a telescope and scale. The 

 telescope and scale, with counterweight and arms carrying the same, are mounted on a 

 ring outside the spindle bearing of the instrument, and may be placed in any azimuth 

 independent of the position of the house of the galvanometer; a suitable lever-clamp is 

 pro^'ided, so that the arms may be clamped in any position. The arms carrying the 

 counterweight and telescope and scale are so arranged that they may be folded against 

 the instrument for transportation; the reading telescope, however, must be unscrewed 

 from its mounting when packing the instrument in its case. The telescope is supplied 

 with a simple reticle of two fibers at right angles. The distance between the object lens 

 of the telescope and mirror is about 25 cm. The scale is on white xylonite, and is 10 cm. 

 long, with graduations at everj^ millimeter; it is mounted somewhat above the horizontal 

 line through the center of the mirror, while the telescope is mounted a corresponding 

 distance below this line. The relations of the scale, telescope, and mirror always being 

 fixed, it is not difficult to find the reflection of the scale, so that the instrument may be 

 quickly set up and adjusted for field use. 



The galvanometer is supplied with an independent tripod, and is clamped in place 

 on this tripod by means of a slip-plate with notches fitting into corresponding grooves in 

 the three foot-screws. 



The instrument case for the entire instrument is made of mahogany, the inside 

 dimensions being 36 cm. wide by 51 cm. long by 14 cm. deep, the material being 1.6 cm. 

 thick. All parts of the instrument, including accessories, the two tripod heads, and the 

 deflection bar are packed in this instrument case, the total weight of which, with the 

 instrument and its accessories, is 15.3 kilograms (see Plate 3, Fig. 2). The net weight of 

 the instrument, with its appurtenances, but not including the two tripod heads, is 7.2 

 kilograms; the two tripod heads weigh 1.1 kilograms, and the instrument box 7 kilograms. 

 The tripod legs for the two tripods are carried separately' in a canvas carrying case, the 

 total weight of the tripod legs and case being 6.8 kilograms. 



DIP INSTRUMENTS. 



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: (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(6); earth-inductor attachment of universal magnetometer type 4(c). Types 

 4(6) and 4(c) have already been described in the preceding pages of this volume. 



