Disturbances of Magnetic Declination in the Kew Observatory. 319 



and not regular occurrence; to prevail contemporaneously everywhere 

 within the limits comprehended by the observations ; and to exhibit 

 a correspondence surprisingly great, not only in the larger, but even 

 in almost all the smaller oscillations ; so that, in the words of the 

 Reporters, MM. Gauss and Weber, " nothing in fact remained which 

 could justly be ascribed to local causes." 



Equally decided were the conclusions drawn against the previously 

 imagined connexion between the magnetic disturbances and derange- 

 ments of the atmosphere, or particular states of the weather. No per- 

 ceptible influence whatsoever on the needle appeared to be produced 

 either by wind-storms or by thunder-storms, even when close at hand. 

 The correspondence in the simultaneous movements of the declina- 

 tion-magnet, so strikingly manifested over an area of such wide extent, 

 was however more remarkable in respect to the direction of a per- 

 turbation than to its amount. The disturbances at different stations, 

 and even, as was expressly stated, at all the stations, coincided, even 

 in the smaller instances, in time and in direction, but with dissimilar 

 proportions of magnitude. Thus it was found generally that by far 

 the greater number of the anomalous indications were smaller at the 

 southern stations and larger at the northern ; the difference being 

 greater than would be due to the difference in the antagonistic 

 retaining force (i. e. the horizontal force of the earth's magnetism, 

 which is greater at the southern than at the northern stations). 

 The generality of this occurrence led to the unavoidable inference, 

 that, in Europe, the energy of the disturbing force must be regarded 

 weaker as we follow its action towards the south. 



A close and minute comparison of the simultaneous movements at 

 stations in near proximity to each other led to the further conclusion, 

 also stated to be unavoidable, that "various forces must be admitted 

 to be contemporaneously in action, being probably quite independent 

 of each other, and having very different sources ; the effects of these 

 various forces being intermixed in very dissimilar proportions at 

 various places of observation according to the directions and distances 

 of these from the sources whence the perturbations proceed." (Re- 

 sultate aus den Beob. des Mag. Vereins, 1836. pp. 99, 100.) The 

 difficulty of disentangling the complications which thus occur at every 

 individual station was fully foreseen and recognized ; and the Report, 

 which bears the initial of M. Gauss, concludes with the remark that 

 " it will be a triumph of science, if at some future time we should 

 succeed in reducing into order the manifold intricacies of the com- 

 binations, in separating from each other the several forces of which 

 they are the compound results, and in assigning the source and 

 measure of each." 



Such was the state of the inquiry when it was entered upon by the 

 Royal Society. The Report of the Committee of Physics drawn up 

 (inter alia) for the guidance of the Magnetic Observatories esta- 

 blished by H.M. Government for a limited period in four of the 

 British Colonies, bears date in 1840. The objects proposed by this 

 Report were a very considerable enlargement upon those of the 

 German Association, as well as an extension of the research to more 

 distant parts of the globe. The German observations had been 



