248 General Sabine — Comparison of Magnetic [May 26, 



have either a local or an atmospherical origin. No connexion or correspon- 

 dence was traceable between the indications of the magnetical and meteoro- 

 logical instruments ; nor had the state of the weather any perceptible in- 

 fluence. It happened very frequently that either an extremely quiescent 

 state of the needle or a very regular and uniform progress was preserved 

 during the prevalence of the most violent storm ; and as with wind-storms, 

 so with thunder-storms, as even when close at hand they appeared to exer- 

 cise no perceptible influence on the magnet. At some of the most active 

 of the Gottingen stations the fluctuations of the horizontal force were ob- 

 served contemporaneously with those of the decUnation-magnet, by means 

 of the bifilar magnetometer devised by M. Gauss : both elements were 

 generally disturbed on the same days and at the same hours. The 

 magnitude of the disturbances appeared to diminish as their action was 

 traced from north to south, giving rise to the conclusion that the focus 

 whence the most powerful disturbances in the northern hemisphere ema- 

 nated might perhaps be successfully sought in parts of the globe to the 

 north or north-west of the area comprehended by the stations. The inter- 

 comparison of the records obtained at the different stations showed more- 

 over that the same element was very differently affected at the same hours 

 at different stations ; and that occasionally the same disturbance showed 

 itself in different elements at different stations. The general conclusion 

 was therefore thus drawn by M. Gauss, that "we are compelled to admit 

 that on the same day and at the same hour various forces are contempo- 

 raneously in action, which are probably quite independent of one another 

 and have very different sources, and that the effects of these various forces 

 are intermixed in very dissimilar proportions at various places of observa- 

 tion relatively to the position and distance of these latter ; or these effects 

 may pass one into the other, one beginning to act before the other has 

 ceased. The disentanglement of the complications which thus occur in 

 the phenomena at every individual station will undoubtedly prove very 

 difficult. Nevertheless we may confidently hope that these difficulties will 

 not always remain insuperable, when the simultaneous observations shall 

 be much more widely extended. It will be a triumph of science should 

 we at some future time succeed in arranging the manifold intricacies of the 

 phenomena, in separating the individual forces of which they are the 

 compound result, and in assigning the source and measure of each." 



In the British investigations, which commenced in 1840, the field of re- 

 search was extended so as to include the most widely separated localities 

 in both hemispheres, selected chiefly with reference to diversity of geo- 

 graphical circumstances, or to magnetic relations of prominent interest. 

 Suitable instruments were provided for the observation of each of the three 

 magnetic elements ; the scheme of research comprehended not alone the 

 casual and irregular fluctuations which had occupied the chief attention of 

 the German associations, bilt also " the actual distribution of the magnetic 

 influence over the globe at the present epoch in its mean or average state. 



