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OBSERVATIONS ON THE AURORA BOREALIS.

In order that our author might not be obscured in his views, he particularly states thedifference between the magnetic effluvia of Halley, and the ferruginous matter of which heconstructs his cylindrical magnetic beams. “ It may perhaps he necessary here, beforethe subject is dismissed,” says Dalton, “ to caution my readers not to form an idea thatthe elastic fluid of magnetic matter, which I have all along conceived to exist in the higherregions of the atmosphere, is the same thing as the magnetic fluid or effluvia of mostwriters on Magnetism. This last they consider as the efficient cause of all the mag-netic phenomena; but it is a mere hypothesis, and the existence of the effluvia hasnever been proved. My fluid of magnetic matter is, like magnetic steel, a substancepossessed of the properties of Magnetism, or, if these writers please, a substance capableof being acted upon by the magnetic effluvia, and not the magnetic effluvia themselves.”

It is somewhat remarkable that, after such an abrupt dismissal of all precedingattempts at explanation, the hypothesis of Dalton should appear the most extravagantthat has hitherto appeared in the history of the Aurora Borealis. We have no know-ledge whatever of the existence of this imaginary ferruginous effluvium; nor wouldany Magnetist ever suppose that such a fluid, even were it admitted to have an exist-ence, would put on the form of cylindrical beams , and at the same time adapt itselfinto rings round the magnetic poles of the earth. Moreover, as this imaginary fluidis supposed to be floating within the atmosphere, the hypothesis is left in a state ofimperfection from a want of information respecting the author’s mode of expandingthe shell of air to the thickness of 150 miles, the height at which he has placed theAurora Borealis.

The same hypothesis supposes that the auroral beams are “ similar and equal intheir real dimensions to one another”—an assertion by no means sanctioned by ob-servation ; but, on the contrary, perfectly at variance with the appearances generally.The hypothesis also supposes that the auroral beams are all “parallel to the dippingneedle at the places over which they appear and that “ the point in the heavens towhich the beams of the Aurora appear to converge at any place is the same as that towhich the south poles of the dipping needle points at that place.” With all duerespect for the philosophical ability and skill of Dr. Dalton, the cause of science hasa predominating claim to our regards over all other considerations in discussions ofthis nature: there can, therefore, be no impropriety in stating that, were there noother observations to discountenance this part of the hypothesis, those on the Auroraof the 17th November last would be sufficient to prove its inaccuracy.

That the auroral arches, when they appear in the north of these latitudes, cross themagnetic meridian at nearly right angles, is a fact very frequently observed, thoughit is by no means its universal position. The highest point of the arch is probably asfrequently in other positions as in the magnetic north: it is sometimes several degreeseastward of the true north, at other times due north, and on many occasions it never