264 REPORTS ON INVESTIGATIONS AND PROJECTS. 



TERRESTRIAL MAGNETISM. 



REPORT OF DEPARTMENT OF RESEARCH IN TERRESTRIAL 



MAGNETISM* 



By L. A. Bauer, Director. 



The advances made during the previous fiscal year in the general 

 discussion of the magnetic observations at present available for an 

 analysis of the distribution of the earth's magnetic forces and of the 

 secular changes laid bare the following fact : 



That until the present material, consisting, as it does, chiefly of 

 observations made on land, and hence derived from only about one- 

 third of the earth, is supplemented by careful and systematic observa- 

 tions over the oceanic areas, conclusions pertaining to the general 

 magnetic conditions of the earth, no matter how skillfully they may 

 have been derived or how plausible they may seem, can not demand 

 entire credence nor be considered as unquestionably established. 



Take for example the result obtained from the investigation of 

 the secular changes in the earth's magnetism, based both on the 

 existing observations and on the best magnetic maps published since 

 1840, " that the secular changes are caused not only by a shift in 

 the direction or position of the earth's magnetic axis, but likewise 

 by a shrinkage in the intensity of magnetization by an annual amount 

 sufficiently large to be readily detectable in the short period of five 

 years." If this conclusion be true it will constitute one of the most 

 important of the many interesting facts concerning the earth's mag- 

 netism, and it will not be without its appropriate bearing on the 

 physical history of our planet. 



However, until the same analysis has been repeated with the aid 

 of observations distributed over the greater part of the earth, no 

 arguments in defense of the theoretical methods used in the analysis 

 of the less comprehensive material will prevail against the vious 

 and easily made criticism of "lack of sufficient data." 



The same state of affairs obtains with regard to the existence or 

 non-existence of electric currents, which are supposed to pass perpen- 

 dicularly through the earth's surface, either coming from outside and 

 entering the earth or coming from within and passing out into the air. 

 The discussion of the data bearing on this question, as set forth in last 

 year's report, would apparently decide in favor of the existence of 

 such currents. But here again the criticism as to lack of data over 

 the great regions embraced by the oceans prevails with full force. 



*Grant No 233. $25,000 for maintenance for 1905. (For first report, see 

 Year Book No. 3, pp. 68-74. ) 



