34 REPORT — 1839. 



This precludes all hope that individuals going about the world 

 from station to station may, by slow degrees, at length amass the 

 information required. It has been ascertained that the mag- 

 netism of the globe is liable to sudden and transient distur- 

 bances, which, so far as appears, are strictly contemporaneous 

 over great districts, and not improbably over the whole surface 

 of the earth. Hence arises the necessity of employing no ob- 

 servations but such as are strictly simultaneous in combinations 

 destined to elicit the values of the magnetic constants, since 

 otherwise the resultant of forces in action at a given point of 

 the globe would be brought into comparison with that of forces 

 which have ceased to act in another point, and thus the in- 

 fluence of local situation would become confounded with that of 

 temporary change. 



Observations prosecuted on such an extensive scale, and so 

 strictly in concert, are altogether beyond the reach of individual 

 zeal and enterprise. They demand a systematic organization 

 and official responsibility quite as much as an outlay of funds, 

 and it is with a view to this that the Association has agreed to 

 the 1st, 2nd, and 3rd Resolutions, which recommend the esta- 

 blishment of what may be called Primary Magnetic Stations, at 

 the places therein named, at points most convenient and appro- 

 priate for combination with the European stations already in 

 activity, including those of Greenwich and Dublin. 



In concert with such primary stations, it would be both natu- 

 ral and highly desirable that travellers provided with the requisite 

 instruments, or officers in other stations who may be willing to 

 devote a portion of their time to this service, and who may for 

 that purpose be temporarily provided with the instrumental 

 means, should act. Every such primary station then, suppos- 

 ing such to be established, would henceforth become a point of 

 reference and comparison, by which short and desultory series 

 of observations in other localities might be rendered available ; 

 including under this head such as might be made in the course 

 of nautical surveys and voyages of discovery, or where from 

 other causes it might be impracticable to remain for any con- 

 siderable time. And it must not be forgotten that from the 

 very peculiar nature of the case, the observations at any one 

 such primary station would be a check upon the fidelity of those 

 made at every other By the help also of such corresponding 

 observations, continued with regularity and steadiness during 

 some considerable length of time, we should be able to ascer- 

 tain whether the means they suggest of determining the dif- 

 ferences of longitude of different stations be really practicable 

 and capable of extension over the whole surface of the globe. 



