TERRESTRIAL MAGNETISM — BAUER. 265 



Were it necessary, other examples might be cited to prove that our 

 progress with regard to the great and principal facts of the earth's 

 magnetism will be at a standstill unless a magnetic survey of the 

 whole globe be undertaken immediately. 



In consequence of these facts it has not been deemed wise to spend 

 very much more effort in further elaboration of the discussion of the 

 present data until some new and unquestioned material has been 

 obtained. 



With the approval, therefore, of the Executive Committee, it was 

 decided to begin the observational work sooner than had originally 

 been contemplated. On account of the large amount of field work 

 undertaken and contemplated during the current year, the office 

 work has necessarily not advanced as rapidly as in the previous year. 

 Nevertheless, satisfactory progress has been made in certain direc- 

 tions, as related below. 



OFFICE WORK PERFORMED. 



Investigation I. — Continuation of the study of the scailar varia- 

 tion and compilation of data a?id preparatioji for publication on a 

 comprehensive, u?iiform plan. — A preliminary communication of the 

 results of this investigation up to the close of last year was pub- 

 lished in the journal " Terrestrial Magnetism and Atmospheric Elec- 

 tricity," December, 1904, under the title "Systems of magnetic 

 forces causing the secular variation of the uniform portion of the 

 earth's magnetism." The following conclusions based upon the 

 present material were reached : 



(i) If we consider simply that portion of the earth's magnetism 

 which may be regarded as equivalent to a uniform magnetization 

 about a diameter inclined approximately 11° to the axis of rotation, 

 then it appears that this portion is subject to a secular variation 

 arising from systems of magnetic or electric forces, two of which are 

 as follows : 



(a) A magnetic system situated below the earth's surface whose 

 axis is directed about opposite to that of the primary internal field 

 and is displaced in longitude at present about 68° to the west. 

 Chiefly as the result of this demagnetizing system, the earth's mag- 

 netic moment is apparenth^ at present being diminished by about 



iWff P^'^^ annually. 



(b) A magnetic system situated above the earth's surface, whose 

 axis is directed almost transverse to the axis of rotation and is dis- 

 placed in longitude at present about 151° to the west of that of the 

 primary internal field and about 83° to the west of that of the inter- 



