of Terrestrial Magnetu m . 1 05 



lies, as we might term therm may present themselves. Should 

 such take place in the phenomena of the solar spots, we have 

 reason to expect that they may be accompanied by correspond- 

 in 2" anomalies in the magnetic variations, if the causal connexion 

 be indeed as close as our late experience would lead us to infer*. 

 Meanwhile the conclusion which we mav most safely draw is that 

 it is highly desirable that both classes of phenomena should be 

 carefully and independently observed and scrutinized. 



In a discover}- so unexpected and so recent as that of the cos- 

 mical connexion of the magnetic disturbances, it cannot be sup- 

 posed that much can yet have become known to indicate the 

 mode in which the sun's influence is exercised in the production 

 of the phenomena of magnetic disturbance which we witness 

 and record. The path in which we may most securely advance 

 towards the attainment of this knowledge is by the careful and 

 continuous study of the effects themselves, and by applying to 

 them such processes of analysis as mat" appear most suitable to 

 aid us in their comprehension. Already by such means we 

 have advanced in a track which promises well, and seems de- 

 serving of being further pursued, and bv a course more svstematic 

 than circumstances have hitherto permitted. The disturbances 

 occurring at a particular station are resolvable, for example, 

 into six distinct categories, — those which deflect the declination 

 needle to the east, and those which deflect it to the west ; those 

 which increase and those which decrease the inclination or dip ; 

 and those which increase or which decrease the intensity of the 



magnetic force. This analysis has been made at a few stations: 

 □ • • 



and the result fully confirms M. Gauss's anticipation that the phe- 

 nomena of each of the different categories would be found to have 

 distinct and independent laws. The research by which these 

 are eliminated may indeed be tedious, requiring both time and 

 labour, and the words of the great geometrician may frequently 

 have to be borne in mind, " It will be a triumph of science 

 should we at some future time succeed in arranging the mani- 

 fold intricacies of the phenomena, in separating the individual 

 forces of which they are the component result, and in assigning 

 the source and the measure of each. ;; That we are advancing 

 in this course, and that the results which have already been 

 obtained merit confidence as true representations of natural facts, 

 may be exemplified by exhibiting in diagrams (Plate I. figs. 1 



* The number of groups of spots observed in 1S56 appears,, from a notice 

 from M. Schwabe in the Astr. Sack., to have been less than might have 

 been expected from the previous decennial progression shown in the Table 

 from \>26 to 1S5' ). The a^gresrate magnetic disturbance in the same vear 

 m the >ertchinsk series. 1851-57 (the only series that 1 have examined 

 which includes 1S56 . exhibits a precisely similar anomaly. 



