112 abstracts: terrestrial magnetism 



at an elevation of about 1 kilomete* a relatively light and warm counter 

 current flows to the east. In reality this is a "land breeze" on a very 

 large scale, so large indeed that per kilometer of coast-line heat energy 

 is converted into wind energy frequently at the rate of 45 million horse 

 power! W. J. Humphreys. 



TERRESTRIAL MAGNETISM.— A new; type of compass declinometer. 

 R. L. Faris. Journal of Terrestrial Magnetism and Atmospheric 

 Electricity 17: 109-114. 1912. 



This paper describes a new form of instrument for ascertaining the 

 magnetic declination at stations where the true bearing to some other 

 point is already known, and is especially adapted for use of general sur- 

 vey parties when working in remote regions, such as Alaska or the Philip- 

 pines, where it is possible at nominal cost to ascertain the magnetic 

 declination much in advance of the possibility of a general magnetic 

 survey. 



E5fperience in the Coast and Geodetic Survey and elsewhere has 

 shown that acceptable magnetic declination results can be obtained with 

 pivot suspension needles. The instrument is described as follows : 



It is essentially a compass needle enclosed in a rectangular needle box 

 with peep sights, which is rigidly mounted on a graduated horizontal 

 circle. The needle lifter and some of the other details are novel and 

 have been worked out with great care. The base rests on three leveling 

 screws and has double centers of brass. The horizontal circle, which is 

 152.4 mm. in diameter, is read by two verniers to single minutes of 

 arc. The needle is mounted in a rectangular box the inside dimensions 

 of which are 164 mm. long, 31.5 mm. wide, and 17 mm. deep. This 

 box is secured to the cover plate of the horizontal circle. At each end of 

 the box is a graduated arc (arc graduated to 10 minutes), about 10° in 

 extent on each side of the zero in the middle. Vertical peep sights, 40 

 mm. high, are attached to the ends of the box so that the zeros of the 

 graduations, the needle pivot and the peep slits are in the same vertical 

 plane. The top edge of the needle is straight, its ends and the apex of 

 the agate cup suspension being in a straight line. The needle lifter is 

 of special design and direct acting, and so arranged that the instrument 

 cannot be packed in its packing case without first lifting the needle off 

 its suspension pivot. When the needle is raised off the pivot it is held 

 firmly in place between the lifter and a flat brass spring in the top of the 

 needle box. The needle and horizontal circle readings are made with 

 the aid of three reading microscopes. The instrument is leveled by 

 means of an adjustable circular level mounted on the cover plate of the 

 horizontal circle. The needle is 148.5 mm. long and is made of "magnet 

 steel;" the dimensions of its cross-section are 0.6 mm. b}^ 3.5 mm. The 

 width of the peep-sight slits is 0.5 mm. 



