346 CARNEGIE INSTITUTION OF WASHINGTON. 



others are then discussed. Langevin's theory of paramagnetism, which, 

 while not an electron theory, is of great importance in connection with such 

 theories, is given in some detail; and the work of Voigt and J. J. Thomson 

 on the diamagnetic and paramagnetic effects of free electron orbits are dis- 

 cussed. The work of Voigt and others on the behavior in a magnetic field 

 of magnetic elements, or magnetons, consisting of homogeneous charged 

 solids or symmetrical electron systems in rotation, is taken up, and some of 

 the most important results of Voigt are given in detail. Considerable space 

 is given to a general theory recently proposed by Gans to account for both 

 diamagnetism and paramagnetism at both ordinary and extreme tempera- 

 tures, and in both weak and strong magnetic fields; and mention is made, 

 with critical comments, of a general theory proposed by Honda and Okubo, 

 and of various attempts to apply the quantum theory to paramagnetism. 

 The paper next deals with the recent direct experimental evidence obtained 

 by the author and Mrs. Barnett, and later and to a more limited extent by 

 Einstein and deHaas, J. Q. Stewart, and E. Beck, on the nature of the mag- 

 neton. The theory involved in this work is briefly given, together with its 

 application to cosmical magnetism. 



A sine galvanometer for determining in absolute measure the horizontal intensity of the 

 Earth's magnetic field.^ S. J. Barnett. 



After a brief historical statement with reference to the measurement of the 

 horizontal intensity of the Earth's magnetic field by electrical methods, and a 

 general description of sine and tangent galvanometers, with the suggestion 

 of an improvement in the latter, a detailed description is given of a new sine 

 galvanometer, constructed, except for certain details, in the instrument shop 

 of the Department of Terrestrial Magnetism. 



The base of the instrument, including the tripod, circles, etc., was taken 

 from one of Wild's theodohtes, constructed by Edelmann, and was much 

 improved by the substitution of non-magnetic parts for parts too magnetic, 

 and by the substitution of electrical illumination of the precision circle for 

 daylight illumination by mirrors. 



The magnetometer-box is of pure copper, the damping being chiefly electro- 

 magnetic. The magnet-mirror is a fine disk of chrome steel with optically 

 flat and parallel surfaces, being in fact one of the gages made by the Bureau 

 of Standards. The torsion tube and head are similar to those of the C. I. W. 

 magnetometers designed and constructed by the Department. A suspension 

 of phosphor-bronze strip with torsional constant 0.001 is generally used. The 

 telescope, which is small but powerful, and the scale, ruled to thirds of milli- 

 meter, on white pyrahn, are provided with all necessary adjustments. The 

 period of the magnet and the damping, which is adjustable, are such that 

 readings require only a few seconds. 



The arrangement of coils is approximately that due to Helmholtz. The 

 spool was machined from white Carara marble impregnated with paraffin 

 at a temperature near its boihng-point. The coils were wound under tension 

 in a single layer in spiral grooves cut with a carbon diamond tool. The wire 

 is pure copper, especially prepared by the Research Laboratory of the General 

 Electric Company. Each coil is wound in two halves and contains 10 turns 

 with a diameter of approximately 30 cm. and a pitch of approximately 2 mm. 

 The two halves start from the same horizontal plane, 180 degrees apart, so 

 that the distance between centers of adjacent wires is approximately 1 mm. 



^Abstract of a paper to be published in full as a special report in Vol. IV, Researches of the 

 Department of Terrestrial Magnetism, Carnegie Institution of Washington Publication No. 

 175, Vol. IV, 1921. A preliminary report was presented before the section of Terrestrial Mag- 

 netism and Electricity of the American Geophysical Union, Washington, D. C, April 18, 1921. 



