DEPARTMENT OF TERRESTRIAL MAGNETISM. 293 



at Vassouras, Brazil. The publication of the results of these inter- 

 comparisons must be deferred until the final determinations of cor- 

 rections, on international magnetic standards at Washington after the 

 return of the instruments used in the comparisons. 



Upon the request of the director of the Batavia Meteorological and 

 Magnetic Observatory, three hygrographs and two hygrograph clocks 

 were purchased at the expense of that observatory and forwarded to it. 



CONSTANTS AND STANDARDIZATIONS AT WASHINGTON. 



Observations, computations, and compilations to determine the con- 

 stants for the instruments in use and their corrections on international 

 magnetic standards,^ as determined by comparisons both at the office 

 and in the field, were kept current. The intercomparisons and stand- 

 ardizations included those for all the instruments to be used on the 

 proposed Cruise VI of the Carnegie begun at Washington, October 9, 

 1919. Simultaneous comparisons of instruments for the determina- 

 tion of constants and corrections were made for 8 magnetometers in 

 declination and horizontal intensity, and for 7 dip-circles and for 5 

 earth-inductors in inclination; corrections in declination were also 

 determined for the compasses of 7 dip-circles, for marine collimat- 

 ing compass No. 1 and for deflector No. 5. Intensity constants were 

 determined and caUbrations made for sea dip-circle No. 189 and T. M. 

 compass variometers Nos. 2 and 4. 



The investigations relating to the sources of error in terrestrial- 

 magnetic instruments and to the causes for apparent changes of instru- 

 mental constants were resumed. The compilations of data for dis- 

 tribution coefficients and temperature coefficients for the different 

 instruments were completed for all of the observations made at Wash- 

 ington, and progress on the corresponding computations and reduc- 

 tions for field observations is now well under way. The results obtained 

 under various conditions and in different fields indicate that the dis- 

 tribution coefficients of a given instrument are practically constant, 

 certainly for long periods, and that deviations from the mean values for 

 individual determinations are in general of an accidental nature. The 

 weighings of magnets with stirrups and determinations of inertia and of 

 induction coefficients for various magnetometers were continued. For 

 a few magnetometers where the corrections on standard determined 

 before and after field work differed materially, the investigations 

 showed that the changes had been caused by alterations in the moment 

 of inertia of the long magnet and its suspension. 



Construction of a sine galvanometer for the absolute determination 

 of magnetic horizontal intensity, and hence superior control of future 

 calibrations, was begun. The general design, as developed by Dr. 

 Barnett, is based on the use of two coils arranged as in the Helmholtz- 



1 See Res. Dep. Terr. Mag., vol. ii, pp. 270-278. 



