GAUSS AND WEBER ON TERRESTRIAL MAGNETISM. 95 



and return to facts. By far the greater number of the ano- 

 malies are found to be smaller at the southern stations, and 

 larger at the northern. For instance, the remarkable ascent of 

 the curve, on the 30th January, 1836, between 9^^ 25"^, and 9"^ 

 40'", amounted in Catania to 6' (reduced to parts of arc) ; in Milan 

 to 12'; in Munich to 13^'; in Leipzig to 16'; in Marburg to 

 20'; in Gottingen to 26'; and at the Hague to 29'. Some- 

 thing, it is true, must be deducted from this inequality, due 

 to the circumstance that, at the northern points (where the 

 horizontal portion of the terrestrial magnetic force has a weaker 

 intensity than at the more southern ones.) similar disturbing 

 forces must produce greater effects ; but the difference of the 

 horizontal intensities at the Hague and Catania is very small 

 in comparison with the inequalities observed ; and it is there- 

 fore certain that the energy of the disturbing force was weaker 

 the further we follow its action towards the south. With all the 

 uncertainty under which we labour with respect to the nature of 

 such distm'bing forces, we cannot doubt that they have some 

 definite source in space ; and, as we must necessarily suppose 

 those which produced the above-mentioned phaenomena to have 

 their seat to the north or to the north-west of the places of obser- 

 vation, (vsithout venturing to define more precisely from so few 

 data,) the northern districts, as far as we may venture to draw 

 any such conclusions from experiments which embrace but a 

 comparatively small portion of the earth's surface, appear to be 

 the great focus, from whence proceed the greatest and most 

 powerful actions. 



A closer inspection of the data hitherto collected leads us 

 to recognise, in the different successive movements, considerable 

 variations in respect to their proportional magnitudes at dif- 

 ferent places, even when the similarity in other respects is un- 

 equivocal : thus, for instance, at one place, the first of two move- 

 ments, following one shortly after the other, is the largest; at 

 another place the reverse happens. We are therefore compelled 

 to admit that, on the same day, and in the same hour, various 

 forces are contemporaneously in action, which are probably quite 

 independent of one another, and have very different sources ; and 

 the effects of these various forces are intermixed, in very dissi- 

 milar proportions, at various places of observation, 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 



