DEPARTMENT OF TERRESTRIAL MAGNETISM. 291 



RESEARCH WORK IN WASHINGTON. 

 TERRESTRIAL MAGNETISM. 



Volume III of Publication No. 175, bearing the title "Ocean Mag- 

 netic Observations, 1905 to 1916, and Reports on Special Researches, 

 by L. A. Bauer, W. J. Peters, J. A. Fleming, J. P. Ault and W. F. G. 

 Swann," already spoken of in the introductory paragraphs of this 

 report, is in the hands of the printer at the end of the fiscal year. 

 Abstracts concerning this volume will be found on pages 326-329. 

 Progress has been made with Volume IV (Magnetic Survey Observa- 

 tions, 1914-1917, and Reports on Special Researches). This volume 

 is to contain both the land and ocean results for the years specified. 



In addition to the pubUcation work and the completion of the 

 investigations contained in Volume III, various investigations, theo- 

 retical and observational, have been carried on, the majority of which 

 are described in the abstracts of papers (pages 318-336). The 

 investigations relating to instrumental improvements, to the designing 

 of new appliances, and to the laws governing changes of constants of 

 magnetic instruments, have been continued (see page 294). The 

 results of some of these investigations are to appear in Volume IV. 



The Director has continued his researches respecting the origin of the 

 Earth's magnetic field, the relation between changes in solar activity 

 and the Earth's magnetic activity, and as to the existence of a possible 

 connection between outstanding astronomical effects and certain 

 cosmic magnetic phenomena. The last question is engaging the 

 attention at present of several noted investigators (see page 321), and 

 it is becoming increasingly difficult to draw a sharp boundary-line 

 between researches belonging distinctively to one or the other of the 

 older sciences. Thus the student of the Earth's magnetism soon finds 

 that he must extend his investigations beyond our planet and take into 

 consideration the existence of cosmic effects of various kinds. 



As one of the first steps, it was considered desirable to attempt the 

 establishment of a theoretical formula which would give an approxi- 

 mate idea, at least, of the possible magnetic field-strength of the main 

 members of our solar system, assuming that the magnetic field of a 

 large body is associated in some manner with speed and direction of 

 rotation. On page 321 a tentative formula is given. If we take as 

 the period of the Sun's rotation that derived from the equatorial 

 motion of sun-spots, etc., the formula gives as the strength of the 

 Sun's magnetic field at its magnetic poles 1 14 times that of the Earth 

 at its magnetic poles. Taking the Sun's rotation period as derived 

 from the Mount Wilson observations, from which the motion of the 

 Sun's magnetic axis about the rotation axis can be deduced, the 

 strength of the Sun's magnetic field, according to the formula, turns 

 out to be 90 times that of the Earth. Hale has deduced from his 



