302 CARNEGIE INSTITUTION OF WASHINGTON. 



The work at Washington has been concerned chiefly with the 

 preparation of manuscript matter for Volume IV, "Researches of the 

 Department of Terrestrial Magnetism," covering the period 1914 to 

 1919. By November 1920 the computations and manuscripts relating 

 to the tabulations of land and ocean results, descriptions of stations, 

 and instrumental constants were completed. There were also prepared 

 for that volume special reports on investigations by members of the 

 division staff. Among the most important of the results are those 

 concerning the constants and corrections of magnetometers and dip- 

 circles. They indicate the necessity of close control, such as is exer- 

 cised by the Department. For magnetometers it is found that gradual 

 changes in inertia of magnet and suspension stirrup take place during 

 field-work and play an important part in the apparent variations 

 with time of corrections on standard. Development by oxidation 

 under field conditions of imperfections on the bearing portions of dip- 

 circle needles cause large variations in the corrections on standard at 

 different inclinations; these variations must be determined by careful 

 examination of needle-differences on the mean from observations with 

 two or more needles at numerous stations. It would seem, in general, 

 advantageous to replace the dip-circle, or at least control it, wherever 

 possible, by an earth-inductor. For most dip-circles, such control, to 

 be really effective, is necessary at intervals of 3° to 5° within the range 

 of inclina,tion covered during field-work. 



Comparisons with standard magnetometer No. 3 and standard 

 earth-inductor No. 48 were made for magnetometer No. 16 and for 

 dip-circle No. 242 during November 1919, after Observer A. Sterling's 

 return from South America. A special series of declination observa- 

 tions was obtained at the Standardizing Magnetic Observatory at 

 Washington during the annular eclipse of the Sun on November 22, 

 1919. Upon the request received by wireless in March from Captain 

 Amundsen, a pair of intensity needles for the dip-circle supplied him 

 was tested and forwarded to Nome, Alaska, where he arrived at the 

 end of July 1920. 



The magnetic observations were reduced which were made by 

 Department observers during the total solar eclipse of May 29, 1919, 

 at Sobral, Brazil, and Huayao, Peru. Considerable time had to be 

 given by Messrs. Wallis and Keulegan to the study and reduction of 

 the variometer results obtained at Sobral and Huayao, where tempo- 

 rary installations of magnetographs had been made. 



All office matters relating to the magnetic-survey operations and 

 observatory work received attention as required. Other miscellaneous 

 work included detailed drawings for instruments and reports, photo- 

 graphing of instruments, classifying and filing of supplies and instru- 

 ments, instruction of new observers in methods of magnetic observa- 

 tions and computations, etc. 



