292 CARNEGIE INSTITUTION OF WASHINGTON. 



preliminary observations that the strength of the Sun's general mag- 

 netic field at its magnetic poles is approximately 80 times that of the 

 Earth at its magnetic poles. It is thus seen that the tentative for- 

 mula agrees with observation as closely as could be expected in view of 

 the uncertainty in the period of the Sun's rotation as a whole. Further- 

 more, Hale thinks it possible that his preliminary value may be in- 

 creased if the Zeeman effect for spectrum lines representing lower levels 

 in the solar atmosphere can be observed. 



Unfortunately, it is not possible at present to test the fonnula 

 further, since we do not know the magnetic field-strength of any other 

 member of the solar system than the Earth and the Sun. It is of 

 interest to note, however, that if the foraiula should receive further 

 verification, it would appear probable that Jupiter may be enveloped 

 by as strong a magnetic field as the Sun, and that Saturn, Uranus, and 

 Neptune may have magnetic fields considerably stronger than that 

 of the Earth. The possibility of decisive laboratory experiments is 

 receiving further attention. 



For additional information regarding above researches, see abstracts 

 on pages 318 330. 



It is appropriate to mention here the loss sustained by terrestrial 

 magnetism in the death of Sir Arthur Rucker on November 3, 1915, 

 in his sixty- seventh year. He was a member of the advisory council 

 of the Department of Terrestrial Magnetism from the time of its 

 estabUshment in 1904. He continued his kindly and stimulating 

 interest practically until the day of his death. His counsel was found 

 exceedingly helpful in determining on the final policy for the conduct 

 of the world-wide work of the Department. In October 1909 he 

 visited the Carnegie at Falmouth, England, and wrote an appreciative 

 letter to the President of the Institution respecting the instruments 

 and methods of work used on the vessel. He also wrote a report 

 entitled "Observations on the magnetic results obtained at and near 

 Falmouth Observatory by the Carnegie Expedition, October 1909." 

 In this report a comparison is made between the magnetic results 

 derived from the Rucker and Thorpe Magnetic Survey of Great 

 Britain and those of the Carnegie expedition. He concluded his report 

 as follows: 



"The agreement of British and Carnegie measurements with each other, 

 whether taken on sea or land, is all that could be desired, even when tested 

 ])y mctliods in which small errors would be at once detected. The net result 

 is to show that two surveys of countries 3,000 miles apart can be connected 

 with each other with almost perfect accuracy, and that sea observations can, 

 in the single case investigated, bo linked up with land observations so as to 

 secure an agreement in the general indications affordetl even by the differences 

 of the differences ))etween the observed and calculated values of the magnetic 

 elements." 



