our earth. Since the laws of meteorology have become better known, and the practice of recording meteorological observations more widely extended, the appearance of Aurora has attracted more attention, especially in its connection with the local variations of the magnetic needle and the disturbances sometimes noticed in the atmospheric electrometers.

Such observations have proved the fact that the Auroral light has been simultaneously perceived over a very extended space; for instance, Auroras in 1831 and 1839 were noticed at the same time, not only in the northern hemisphere, but also in the southern. Tables of the comparative frequency of the appearance of Auroras in different places point out the arctic zone, however, as that in which these phenomena most frequently occur.

Electricians and astronomers have endeavoured to ascertain the height of the Aurora above the earth, especially by measuring the height of the arc of the Aurora at different places, but as their observations were taken from different points of view, probably, each observer saw his own particular arc, and the results are, therefore, discordant. Thus, of two observers who calculated the height of the Aurora in January, 1831, one made it 18 miles-the other, 96.

The ancients supposed the height of the Aurora to be very great-even beyond our atmosphere-but later observers reduced it to 75 miles; thus, Cavendish supposes its usual elevation to be about 71 miles above the earth, at which elevation the atmosphere must possess but 15th part of the density of that at the earth's surface. Still more modern observers think it does not rise above the region of the clouds; and Wrangel, Struve, Parry, Fisher, and others, ascribe to it a very inconsiderable height.

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Very valuable observations have been made by different persons in Aberdeenshire, tending to prove that, at times, its height is not more than half a mile above the surface of the

earth. Parry, in January 7th, 1825, whilst watching the variations in the form of an Aurora, saw a ray of light dart down from it towards the earth, between himself and the land. which was about 3,000 yards from him; this was also witnessed by two of the officers of the expedition. I believe I am correct in stating that many of the arctic observers believe the Aurora to attain a very inconsiderable elevation in high latitudes. Hood and Richardson observed the same Aurora from different places: to the one it appeared in the zenith, forming a confused mass of flashes and beams-to the other, at many miles distant, looking in the same direction as the first observer, it presented the aspect of a low illumined arch. Sir William Hooker informs me that while passing a night on the summit of Ben Nevis, he distinctly saw the Aurora hanging in the valley between a neighbouring elevation and that upon which he stood; also that, at another time, during a fall of snow upon a mountain side, he observed that the particles were distinctly luminous, the air giving evidence, at the same time, of the presence of much free electricity. General Sabine also tells me that he has seen the Aurora low down, and passed through it, as one would walk through a mist. On the nights of the 30th and 31st March, 1859, I noticed the Aurora between myself and the land. The patches of light could plainly be seen a few feet above the surface of the water in Bellot Straits, the opposite land being about 2 or 3 miles distant; and I am confident that if that land had been sufficiently high, the greater number of the 24 Auroras seen during the winter of 1858-9 above the water space in Bellot Straits, if not all, would have been seen suspended at a low elevation above the water or ice. To give as accurate a description as possible of my own experiences of Aurora, I transcribe from my journal, verbatim, the following extracts, to show some of the data upon which remarks are founded:my "Nov. 9, 1857 11 p.m. I have just come down from deck,

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where I saw one of the finest Auroras we have had as yet-it extended for about 90°, being about 7° above the horizon-of a colour changing from a pale yellow to pale green, with vertical streamers towards the zenith; it seemed to appear just above a misty or foggy bank, which gradually enlarged till it obscured the Aurora; there were no vibrations or oscillations, but at times the Aurora was broken up into detached pieces; it was from S. to W., and lasted for an hour and a quarter.

Nov. 23. A pale, yellow Aurora appeared this evening for about an hour in the N.W. horizon, with occasional streamers rising 6° to 7° towards the zenith; it was rather vacillating in its character whilst it was visible; it was situated between Saturn and Jupiter. Another very bright one has just appeared from N.W. to S.E.; it was by far the brightest yet seen, and of a pale green colour; it appeared generally in arcs about 10° above the horizon; these arcs seemed to be composed of centres of effulgence with light spreading from the sides, and streamers stretching 20° towards the zenith; at other times broken up into detached pieces like the glow discharge of the electrical machine, sometimes divided into three tiers of arcs, all having streamers.

Wednes. Dec. 16th. Going upon deck at 9 p.m., noticed a hazy luminosity all over the sky; about 9.15 the Aurora presented itself; it commenced in the S., and then passed in a horizontal band to E., from that it passed to N. and N.N.W.; south joining north by a band through the zenith; E. also joining N.N.W. by a similar band. Three or four times I noticed a distinct pulse passing from S.E. to E., and from E. to N.; at times the merry dancers appeared, but at no time was there a brilliant appearance, only a universal luminosity; bands and conglomerate masses prevailed, but a few arcs appeared towards and round the zenith; there was a little wind and the pulsations seemed to go contrary to it. The

stars which were studding the sky were perceptibly dimmed— no sounds were heard-the colour was from a very pale yellowish green to a pale pink; it remained apparent for abou 15 minutes, after which the atmosphere was filled gradually by a mist; the luminosity formed no definite shape, except the few arcs spoken of; they only had pink; temp.—14°, bar. 29° 80.

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Thurs., Dec. 17th, at 6.30 p.m., observed a faint Aurora from S.S.E. to E.; nothing particular about it; died out about 7.15. At 10 p.m., observed a bright Aurora, extending from S. to N.N.E.; a low bank of fog, 5° above the horizon, formed the edge of an arc, about 1° broad; 2° above this, another arc was situated, about 4° broad; these changed into broad luminous clouds at times, and then, again, formed a thin, long, arc, extending continuously from S. to N.N.E., with streamers ascending 8° to 10° towards the zenith; the colour generally a yellowish green, but once it was quite reddish in the E.; at this point, the Aurora was most intense and constant. again noticed the pulse wave; it oscillated from S.S.E. to E.; the "merry dancers" sometimes was the form assumed; once or twice there was an instantaneous intensity in the light of the whole mass, and as quick a relapse to the original. In the thick body of the Aurora the light was so intense as completely to hide the appearance of stars of the first magnitude—through the streamers the stars showing, although but dimly; it is still visible; (12 p.m.) since its appearance the wind has increased; temp.--21°. At 11 o'clock, I noticed a falling star of a very bright character; it descended from 35° above the horizon and below Saturn, towards the horizon, but, on approaching the Aurora, it was dimmed, and then completely obscured; when it came to the thick band it left a tail 2° behind it—it fell very slowly. No sounds were heard with the Aurora; those bands which did appear were as luminous as those of last night, but were more confined to one part of the sky.

(12 p.m.) Still continues, more concentrated, and a little brighter; dense streamers, longer and altogether higher above the horizon. (4 a.m.) The Aurora still brilliant, and in the same direction, but forming more of an arciform shape, and changing sometimes to a reddish hue. (9 a.m.) Still apparent, -now crosses the zenith-not in streamers, but more in shapeless patches of thin light, across the zenith from S.W. to W. and W.S.W.; also, from E. to N.W., a broad band about 70° above the horizon in E., very persistent against the blue black ground; the stars are visible through it. Minute spicula of snow visible through the atmosphere.

Friday, 18th. As the daylight increased, the Aurora became less visible, and at 10 a.m., it was not seen, but, in its place, thin, fleecy clouds appeared, just as if it had been the cloud which had been rendered luminous. Everything having been prepared, at 10.30 a.m., whilst the cloud still remained, I connected an electrometer with the copper chain in the observatory, when distinct separation of the gold leaves took place. At 6 p.m., an Aurora was visible from E. to W. and N.W. across the zenith; it was in the form of bands or streamers. I again tried the electrometer, and again perceived distinct divergence of the gold leaves; this Aurora disappeared about 7 p.m. Again, at 8.30, there was an Aurora, stretching from S.S.W. to S.S.E., in the form of a bent arch or horseshoe, the key being in the S.S.E. Again, the electrometer was connected, and a still greater divergence of the gold leaves than before was noticed; this might be accounted for by the greater luminosity of the Aurora. I tried paper, saturated with iodide of potassium, interposed between two platinum wires, connected with the chain and the water, but no decomposition took place, and no spot was obtained. (12 p.m.) This Aurora is still visible, but with no particular shape; it extends from S.S.W. by S. to N., and not only horizontally, but towards the zenith, scintillations appear; it is most luminous towards the