REPORT OF EXECUTIVE COMMITTEE. 69 



render service, to rent modest private quarters in addition to those 

 furnished in the Coast and Geodetic Survey Office. Such other 

 requisite facilities as were possible were readily and courteously 

 furnished by the Superintendent of the Coast and Geodetic Survey 

 for the furtherance of the work of the department ; thus instruments 

 and books were loaned, and training in observation and computing 

 was given to certain employees. 



OFFICE WORK PERFORMED. 



Investigation I. A general compilation and discussion of magnetic data 

 for the complete presentation of our existiug knowledge of the secular 

 variation of the earth's magnetism over the entire globe, with the view of 

 determining the points at which it will be necessary to repeat observations 

 at suitable intervals, for the successful scientific investigation and deter- 

 mination of the cairses and their modes of action, and for ascertaining the 

 proper corrections to magnetic charts to refer them to a desired date. 



This investigation is in progress and will require some time for 

 completion. It involves a number of initial, related researches for 

 furnishing the necessary data and methods so as to permit exhibit- 

 ing and publishing the results on a consistent and homogeneous 

 basis. Thus, frequently a critical study of the observer's methods 

 and instruments must be made in order to furnish clues for the in- 

 terpretation of discrepancies either between his own results or be- 

 tween his and those of another observer at the same station. So 

 also it has been found necessary to make a critical study of the 

 existing magnetic maps since those of Sabine for 1840-45, with the 

 view of exhibiting the state of our existing knowledge of the distri- 

 bution of the magnetic forces and of the secular changes. Like- 

 wise, in order to furnish the necessary reduction corrections to the 

 observed quantities, it was requisite to make a compilation of data 

 pertaining to the diurnal variation of the magnetic elements and to 

 determine the laws governing their geographical distribution. 



From these correlated studies useful permanent information has 

 been obtained and certain interesting and important results deduced, 

 of which the chief ones are : 



Comparatively little increase in our knowledge of the gen- 

 eral distribution of the earth's magnetic forces has been made 

 during the past half-century, in consequence of which certain 

 constants requisite for the theory of the earth's magnetism are 

 not known at present with any greater degree of certainty than 

 for the epoch of the construction of Sabine's charts (1840-45). 



