after noon, and descending in the following hours of the forenoon; there is, on the other hand, scarcely a trace of this in the three winter terms, Plates IV. V. and IX. All our experience shows that partial or even total obliteration of the regular movements by the irregular is a very common occurrence. In the years 1834 and 1835 some terms occurred in which the regular course was not at all obscured by any considerable anomalies, although there was no want of smaller ones. But what renders the anomalous oscillations so remarkable, is their extraordinary coincidence, generally even in the smaller instances, at different stations; nay, commonly at all the stations, only in dissimilar proportions of magnitude. It is quite unnecessary to demonstrate this agreement in individual instances: a view of the representations of the six terms will speak sufficiently for itself.
We cannot at present decipher these enigmatical hieroglyphics of nature: we must first endeavour to procure from the most diversified sources, authentic, numerous, and minutely faithful copies, in the confident hope, that when these rich materials are accumulated, the key to their hidden meaning will not be long wanting. In the mean time I may be allowed to add a few remarks, which may assist in the formation of a more correct judgement concerning them.
First, it must not be forgotten that these anomalies are but comparatively small modifications of some of the effects of the great terrestrial magnetic force; that we must distinguish between the force itself and these supervening alterations; and that nothing in the present state of our knowledge obliges us to ascribe both to the same or to similar causes. Therefore those who think it probable that these anomalies are the effects of electric currents, or of action, perhaps far beyond our atmosphere, (which view we leave entirely to its own merits) may continue to do so, without having to relinquish on that account the old view, of a force, residing in the solid portions of the earth, or rather being the collective action of all its magnetized particles. If, according to the opinions of some philosophers, the interior of the earth be supposed still in a fluid state, the constantly advancing solidification, and the consequent thickening of the solid crust of the earth, would offer the most natural explanation of the secular variations of the magnetic force.
But we willingly leave the uncertain ground of hypothesis,
