DEPARTMENT OF TERRESTRIAL MAGNETISM. 297 



cause of the comparative remoteness from continental masses. The result 

 indicated an upward positive electric current of average strength of only 

 nine-thousandth ampere per square kilometer. 



The fifth line-integral is for the Carnegie's subantarctic cruise from Decem- 

 ber?, 1915, to March 31, 1916, between the parallels 40° and 60° south, and 

 inclosing a polar area of 50,236,934 sq. km. This circuit incloses a region 

 high and mountainous in the center, of perpetual snow and glaciers, where 

 winds of unusual force prevail and where the atmospheric conditions are 

 considerably different from those of the previous cases. The line-integral 

 indicated an upward positive electric current of average strength one-sixtieth 

 ampere per square kilometer. 



The results of the line-integrals for these five ocean areas are in general 

 accord with those given in the first author's 1920 paper (Terr. Mag., vol. 25, 

 pp. 151-156, December 1920). They show a consistent and possibly a signifi- 

 cant geographical distribution in magnitude as well as algebraic sign. 



An investigation was likewise made as to what extent certain assumed 

 errors in the data used for the calculation of these line-integrals would affect 

 the final result. It was found that accidental errors of observation even larger 

 than might be expected would not effect the values of the integrals materially. 

 Mr. Ennis and Miss Tibbetts assisted in all these computations. 



Dip-needle errors arising from minute pivot-defects.^ H. W. Fisk. Special report in Vol. 

 IV of Researches of Department of Terrestrial Magnetism, Carnegie Inst. Wash. 

 Pub. No. 175, Vol. IV, 359-371, 10 text-figures (1921). 



In determining inclination by means of a dip circle, four needles are ordina- 

 rily used. There is reason to believe that there is a constant correction that 

 applies to a given instrument with a specified set of needles, and there are, 

 furthermore, characteristic variations among individual needles probably 

 arising from mechanical imperfections. These are found to vary slightly 

 with the magnetic field and may be determined by least-square reductions 

 when data are sufficient. 



It often occurs that within a limited range of inclination a needle will give 

 results that do not harmonize with its general behavior, and it has been the 

 practice to reject such erratic values. In this paper a special study has been 

 made of certain cases of this kind, and it has been found that the erratic 

 values do not occur indiscriminately, but the corrections required to bring 

 them into harmony with the other needles take a symmetrical form resembling 

 a sine-curve when plotted for the range of inclination over which the erratic 

 values are found. This range is, in general, about 4° or 5°, and the amplitude 

 of the correction-curve represents from 6' to 10'. This form of curve suggested 

 the possibility that the trouble was caused by a minute particle adhering to 

 the pivot. A theoretical discussion is made of the effect of such a particle 

 under varying conditions, and the results are compared with those found 

 from the observations. The general correspondence between the theoretical 

 and observed results leads to the conclusion that minute rust-particles, which 

 may suddenly appear and later disappear, may be of the form and magnitude 

 required to produce the observed effects. 



A series of diagrams and graphs accompanies the article, and a table is given 

 illustrating the method used in analyzing the observational data in order to 

 separate the affected value from the others. 



> A paper under this title was also presented before the Philosophical Society of Washington 

 on November 19, 1921; see Jour. Wash. Acad. Sci., vol. 12, 21-22 (January 4, 1922). 



