ceased. The disentanglement of the complications which thus occur in the phænomena 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 phænomena,—in separating the individual forces of which they are the compound result,—and in assigning the source and measure of each. Now and then we find at some places a small change, without any apparent counterpart at any of the other stations. Such occurrences ought not to be at once looked upon as evidences of local magnetic action. In so great a mass of numbers an error may sometimes take place. Cases have frequently occurred to us where a revision of the original observations, when these were in our hands, has shewn an error of calculation in the reduction, or an evidently accidental error in the writing. In other cases, in which we had received only an extract of the observations, a reference to our correspondent has led to a similar conclusion. As, however, it is impracticable to discuss all such cases by correspondence, those observers who do not communicate the original observations are requested, when they discover such cases in the curves representing them (as, for instance, at Leipzig, on the-26th of November, 1836, for 6h 15m Göttingen mean time), to refer to the original register. If errors are thus discovered, they can be corrected in a following number. Even when the original papers do not decidedly indicate any error, yet we cannot have perfect assurance with respect to cases which rest only on a single set of observations: it may happen, even to a practised observer, to write down in the same set repeated erroneous decimals. By such a conjecture, (somewhat hazarded it is time,) the above-mentioned number 11·69 would be reduced to 6·69, and thus correspond with the others.
But supposing the case of such an insulated movement to be established beyond all doubt, it does not follow that it is to be considered as local in the most limited sense. As the source of every anomaly must have its seat somewhere, it may be that the disturbing force is in the neighbourhood of the station itself. If feeble, its action may still be perceptible at that station, on account of its proximity, and may disappear (i. e. be no longer
