the Pole, and within the ring, the nearest and highest part of the ring will be seen to the south, just as the ring of the aurora borealis was seen at Good Hope. Now, were the pole of the earth, or rather a point of its lengthened axis, the centre of the ring of the aurora borealis, the highest point of the arch would be seen every where in the true meridian, or due north. But, as this is not the case, since, with us, the highest point of the arch is seen about 20° west of due north, in North America it is seen due north, and at Good Hope, in Greenland, to the east, it follows that the centre of the ring must lie about from 20 to 30 from the Pole of the earth, in a meridian passing through the States of North America :-and since the arch is sometimes seen in the zenith near Iceland, and often stretches so far to the south as to pass the zenith, both here, in Christiania and in Copenhagen, and even in more southerly regions, it follows that the radius of the ring of the aurora borealis may extend from 20° to 40° and above.

It is easy now to perceive in what manner the arch of the aurora borealis will appear in different meridians. If it be viewed from a point lying in the same meridian with its centre, its highest point will appear due north; and if this rise so high as to pass through the zenith, its extremities will terminate in the east and west. If, again, it be viewed from a point lying eastward of the meridian of the ring, as with us in Europe, then the highest point of the arch will move to the west of the meridian, and the farther, the more you advance to the north, till you come to the same latitude with the centre of the ring, between 60° and 70°. Here the highest point of the arch will lie due west; and if the ring extend so far as to pass through the observer's zenith, it will go from north to south, that is, it will be parallel with the meridian. Such was the case with regard to the arch seen by Captain Scoresby on the 15th of April, in Lat. 64° 41'. If the place of the observer be within the circumference of the ring of the aurora borealis, as is the case with the colonies in the western districts of Greenland, the arch will he seen to the south, provided the observer be south from its centre, and to the east, if he be east from it. These rules may be shortly expressed in the following formula. If the observer be on the outside of the ring of the aurora borealis, he will see the highest point of the arch in the same direction with the centre of the ring: if he be within the ring, the highest point of the arch will

be seen in the direction opposite to that of the centre of the ring.*

That the centre of the ring of the aurora borealis does not coincide with the north pole of the earth, is a very remarkable fact. This centre coincides as near as possible with the magnetic pole in North America, the place of which we have determined in the first volume of this Journal. From this, we are led to suppose that there must be some connexion between the aurora borealis and the magnetism of the earth. This conjecture is strengthened by the observations of Captain Cook with respect to the aurora australis. When that celebrated navigator, on his second voyage, was sailing round the South Pole, he often saw, in the southern parts of the Indian sea, arches of the aurora australis, the highest point of which always lay to the southeast, so long as the ship sailed between the meridian of the Indian Peninsula and the parallel of 60°. In that region the variation of the compass is between 30° and 40° W. The highest point of the arch of the aurora ' australis coincides here too with the direction of the needle. But as soon as he approached the meridian of Van Dieman's Land, where the variation of the compass disappears, the highest point of the arch of the aurora australis was found, too, in the true meridian. From this it appears that the centre of the ring of the aurora australis likewise lies at a considerable distance, from 30° to 40°, from the south pole of the earth, and in a meridian which passes through New Holland. And here, too, we have shewn in the first volume of this Journal, is the south magnetic pole to be found.

If there be now an actual connexion between the polar lights and the magnetism of the earth, we should expect to find similar luminous rings, or at least powerful exhibitions of the polar light in the northern parts of Siberia, and in the neighbourhood of Terra del Fuego, that is, at the two extre

* Accounts with regard to the appearances of the aurora borealis in Easter Finmark, as well as observations important to the physical science of the globe in general, are expected from Dean Deinboll, and with the more eagerness, that these tracts are seldom visited by men of science, who, besides, when they do visit them, hurry back, after a short survey, from regions, the winter of which the inhabitant of the south views with horror.

+ Christiania Mag. of Nat. Hist. p. 19.

Christiania Mag. of Nat. Hist. p. 32.

* Parish clergyman at Vadsoe, near Wardhuus (the most northerly parish in Europe), and lately a much respected and patriotic member of the Norwegian Storthing.-TR.

mities of the weaker magnetic axis of the earth. And we find that this is in reality the case. Gmelin gives a splendid, almost a terrific, description of the brilliancy of the aurora borealis, as it is scen in the north of Siberia, along the coasts of the Frozen Sea, between the rivers Jemsei and Lena, adding, that "here seems to be the true native country of the aurora borealis." The same thing says Horrebow, concerning Iceland; and the author of the Mirror for Kings, together with all later observers down to Ginge, concerning Greenland. We find thus, that, in the northern hemisphere, the polar lights have two different centres, one in the north-west, lying in the neighbourhood of Hudson's Straits; another in the northeast, lying in the Frozen Sea, north from Siberia. When Captain Cook sailed round the South Pole, he saw no where the aurora australis, except in the tract we have just mentioned, in the Southern Indian Ocean; but the Spanish navigator, Don Antonio de Ulloa, mentions, in a letter to Mairan, that, when he sailed past Cape Horn, in Terra del Fuego, as often as the thick fog which prevailed there allowed him to see but a little beyond the ship's head, he always observed a perceptible illumination towards the south or southwest, which had altogether the appearance of the polar lights so well known to him in the northern hemisphere. The Abbé Molina, too, in his description of the Chiloe Isles, which lie a little to the north of the southwest coast of America, asserts, that the aurora australis was frequently seen there. It appears, therefore, that the polar lights spring from four points on the surface of the earth, which, so far as we have hitherto been able to determine, coincide with the magnetic poles of the earth. The larger luminous ring is formed round the two opposite poles of the stronger magnetic axis in North America. and New Holland. Whether a similar ring, as full and as regular, be formed round the poles of the weaker axis in Siberia and Terra del Fuego, is a matter which, from the few observations we are able to collect, cannot yet be so well

ascertained.

The arch of the polar light is seldom seen without luminous beams shooting out from it. From the side of the arch turned away from the Pole, beams or rather columns of light dart forth in a direction nearly perpendicular to the arch, and ascend towards the zenith. If these beams are so long as to pass a considerable way beyond the zenith, towards the south, they form, in the neighbourhood of the zenith, a kind of corona

Such I

or glory, which seems to be the point of their union. This corona lies from 15° to 20° south of the zenith, in such a situation, that if we suppose a vertical plane passing through the highest point of the arch, which with us lies about 20° west from the meridian, and produced so as to pass through the zenith, it will come exactly upon the middle of the corona. And it is a very remarkable circumstance, that the distance of this corona from the southern horizon, is exactly equal to the inclination of the needle at the place; so that the south pole of the needle points directly to the centre of the corona. found to be the case with regard to a pretty full aurora borealis, on the 7th of October, 1816. The height of the crown was 73° 10′; its eastern azimuth 12° 11'. With regard to another, on the 8th of February, 1817, the height of the corona was 74° 39′; its east azimuth 14° 57'. Now, in Christiana, the variation of the compass is 20°, and the inclination. of the needle about 73°. It will be understood, of course, that we cannot determine, with perfect exactness, the situation of so changing a mass of light; and that, therefore, the sinall deviations from the direction of the needle cannot be taken into account. At the moment when the corona is formed, and the whole heavens have the appearance of a brilliant cupola, supported by columns of different coloured light, the aurora borealis displays its full beauty and majesty. Such exhibitions of these lights, which, in the period from 1720, to about 1790, were pretty frequent, have of late years been very rare; and we live in one of the great pauses of this brilliant phenomenon. We often see but a portion of an arch; sometimes shooting beams without an arch; and sometimes only a faint glimmering towards the north, without distinguishable beams.

To give the optical explanation of the corona, would be a subject too extensive for us to enter on. I shall only briefly state here, that the formation of the corona can only be explained, by supposing that the luminous columns shoot from the surface of the earth in a direction parallel to the inclination of the needle, and to the direction of the earth's magnetism; that they first become luminous when they pass out of our atmosphere; while, in passing through it, they have the opposite effect of rendering it opaque. By this, we can explain the dark segment which appears under the arch; and also this remarkable fact, that, while the aurora borealis is in play, the sky, which is now perfectly transparent, may, in less than

a minute of time, be covered with an almost impenetrable veil, which again may vanish in a time as short,—a circumstance which, in our northern regions, may very unexpectedly derange many an astronomical observation. By this supposition, too, we can explain the dark-coloured streaks of the aurora borealis, which I myself have frequently observed, and which are mentioned by several persons who have described these lights in Norway. If we turn the eye towards the magnetic zenith (if I may be allowed to give this name to that point in the heavens to which the higher, or, with us, the southern pole of the needle points), we here see the luminous columns from the end; and, as they are at a considerable distance from one another, in this situation the eye perceives the blue arch of the heavens between them. In all other parts of the sky, we see the luminous columns obliquely; so that the one covers the other, which consequently gives them the appearance of beams darting from the arch, connected in onebody. The following figurative illustrations may make this plain. Suppose a person lying in a field of rank grass, or in a forest of tall pines, he will, in this case, see only a circular portion of the sky round the zenith. The lower part of the sky cannot be seen, concealed by the close standing stalks of the grain, or by the stems of the trees, which cover one another. If we hold a brush or a close heckle in such a manner that the bristles of the one, or the teeth of the other, are turned to the eye, round that place where the direction of the bristles or the teeth coincide with the axis of the eye, we can perceive the bottom of the brush or the heckle. In all other places, the bristles and the teeth cover one another, and conceal the bottom. If we now suppose a plane reaching the heavens, in the magnetic zenith which I have mentioned, and that the luminous columns shoot up perpendicularly to this plane, it will now be easy to perceive, from these examples, why the luminous mass can be seen through in these places, and forms a sort of corona, towards which all the beams seem to collect. When the arch of the aurora borealis rises so high in the sky as to reach the magnetic zenith, it seems then, at this place, to be broken off, from which we may infer, that the rings of the polar lights consist of very short luminous cylinders, parallel to the direction of the magnetism of the earth, which seem only to form one connected luminous mass, because the intermediate spaces are filled up by rows of luminous vlinders lying behind one another. We see also from this,