Imatges de pÓgina

What is the origin of these remark- end of the phenomenon. The rays then able phenomena ? The ancients asked become more rare, shorter, and less vivthe question, and the moderns reply by idly colored. Soon nothing further is repeating it. Before proceeding to de- seen on the celestial vault than wide, scribe the magnificent auroral displays of motionless, nebulous spots, pale, or of August 28th and September 2d, let us an ashy color; they have already disexamine authorities upon this subject, appeared, when the traces of the dark and see if we cannot arrive at some sat- segment whence the appearance originisfactory solution of the phenomena. The ated still remain on the horizon." following is the description given by Hum- The connection that seems to exist, boldt in Cosmos”:

says De la Rive, between the polar light “ An aurora borealis is always preced- and the appearance of a certain species ed by the formation in the horizon of a of clouds is confirmed by all observers ; sort of nebulous veil, which slowly ascends all have affirmed that the polar light to a height of 4°, 6°, 8°, and even to 10°. emitted its most brilliant rays when the It is towards the magnetic meridian of high regions of the air contained heaps the place that the sky, at first pure, be- of cirri, -strata of sufficient tenuity and gins to get brownish. Through this ob- lightness to cause a corona to arise around scure segment, the color of which pass- the light. Sometimes these clouds are es from brown to violet, the stars are grouped and arranged almost like the seen, as through a thick fog. A wider rays of an aurora borealis; they then arc, but one of brilliant light, at first appear to disturb the magnetized needle. white, then yellow, bounds the dark seg- Father Secchi has remarked, that magnetment. Sometimes the luminous arc ap- ic disturbances are manifested at Rome pears agitated, for hours together, by a whilst the sky is veiled with clouds that sort of effervescence, and by a continuous are slightly phosphorescent, which, at change of form, before the rising of the night, present the appearance of feeble rays and columns of light, which ascend auroræ boreales. as far as the zenith. The more intense After a brilliant aurora borealis, we the emission of the polar light, the more have been able to recognize, on the folvivid are its colors, which, from violet lowing morning, trains of clouds, which, and bluish white, pass through all the in- during the night, had appeared as so termediate shades of green and purple- many luminous rays. red. Sometimes the columns of light The absolute height of auroræ boreales appear to come out of the brilliant arc has been very variously estimated by mingled with blackish rays, resembling a different observers. It has long been thick smoke; sometimes they rise simul- thought that we might determine it by taneously from different points of the ho- regarding, from two places widely distant rizon, and unite themselves into a sea from each other, the same part of the of flames, the magnificence of which no aurora,—the corona, for example. But painting could express ; for, at each in- we have started from a very inaccurate stant, rapid undulations cause their form assumption, namely, that the two oband brilliancy to vary. Motion appears servers had their eyes directed to the to increase the visibility of the phenome- same point at the same time, -- whilst it na. Around the point in the heaven is now well proved that the corona is which corresponds to the direction of the an effect of perspective, due to the apdipping needle produced, the rays ap- parent convergence of the parallel rays pear to meet and form the boreal coro- situated in the magnetic meridian ; so na. It is seldom that the appearance

that each observer sees his own aurora is so complete, and is prolonged to the borealis, as each sees his own rainbow. formation of the corona; but when the The aspect of the phenomenon depends latter appears, it always announces the also upon the positions of the observers. The seat of the aurora borealis is attempted to establish that there were in the upper regions of the atmosphere; fixed epochs for its display in the highest though sometimes it appears to be pro- degree of brilliancy. The length of these duced in the less elevated regions where periods was from sixty to seventy years, the clouds are formed. This, at least, and the next appearance was to be in is what follows from some observations, 1890. The remarkable displays of Auespecially from those of Captain Frank- gust 28th and September 2d show the lin, who saw an aurora borealis the light fallacy of his conclusions in this respect. of which appeared to him to illuminate Mairon and Dalton had also thought the lower surface of a stratum of clouds; that the aurora borealis was a cosmical, whilst some twenty-five miles farther on, and not an atmospheric phenomenon. Mr. Kendal, who had watched the whole But M. Biot, who had himself had an opof the night without losing sight of the portunity of observing the aurora in the sky for a single moment, did not per- Shetland Isles in 1817, had already been ceive any trace of light. Captain Par- led to recognize it as an atmospheric ry saw an aurora borealis display itself phenomenon, by the consideration that against the side of a mountain ; and we the arcs and the coronæ of the aurora in are assured that a luminous ring has no way participate in the apparent mo sometimes been perceived upon the very tion of the stars from east to west,-a surface of the sea, around the magnetic proof that they are drawn along by the pole. Lieutenant Hood and Dr. Rich- rotation of the earth. Hence, almost all ardson, being placed at the distance of observers have arrived at the same conabout forty-five miles from each other, clusions; we will in particular cite MM. in order to make simultaneous observa- Lottin and Bravais, who have observed tions, whence they might deduce the more than a hundred and forty auroræ parallax of the phenomenon, and conse boreales. It is therefore now clearly quently its height, were led to the con- proved that the aurora borealis is not an clusion that the aurora borealis had not extra-atmospheric phenomenon. To the a greater elevation than five miles. M. proofs drawn from the appearance of the Liais, having had the opportunity of ap- phenomenon itself we may add others plying a method, which he had devised deduced from certain effects which acfor measuring the height of auroræ bo- company it, such as the noise of crepitareales, to an aurora seen at Cherbourg tion, which the dwellers nearest to the Oct. 31, 1853, found that the arc of the pole affirm that they have heard when aurora was about two and a half miles there is the appearance of an aurora, above the ground, at its lower edge. and the sulphurous odor that accompanies

Various observations made by Profes- it. Finally, if the phenomena took place sor Olmsted, in conjunction with Profes- beyond our planet and its atmosphere, sor Twining, of New Haven, led him, why should they take place at the polar on the contrary, to fix the elevation regions only, as they often do? on different occasions at forty-two, one J. S. Winn, in a letter to Dr. Frankhundred, and one hundred and sixty lin, dated Spithead, August 12th, 1772, miles. He claims that it is rarely less says: “ The observation is new, I bethan seventy miles from the earth, and lieve, that the aurora borealis is connever more than one hundred and sixty stantly succeeded by hard southerly or He also claims that its origin is cosmi- southwest winds, attended with hazy cal,- or, in other words, that the earth, weather and small rain. I think I am in revolving in its orbit, at certain pe- warranted from experience in saying conriods passes through a nebulous body, stantly, for in twenty-three instances that which evolves this strange light in more have occurred since I first made the ob or less brilliancy, as the body is larger servation it has invariably obtained; and or smaller. To support this theory, he the knowledge has been of vast service to me, as I have got out of the Channel or crepitation, when the vessel he was when other men as alert, and in faster on board was in the midst of an auroships, but unapprised of this circumstance, ra borealis. This was also observed in have not only been driven back, but with many localities during the aurora of Audifficulty escaped shipwreck."

gust 28th, 1859. A New York paper, Colonel James Capper, the discoverer alluding to the subject, remarks: “Many of the circular nature of storms, remarks: imagined that they heard rushing sounds, “ As it appears, that, on all such occasions, as if Æolus had let loose the winds; oththe current of air comes in a direction ers were confident that a sweeping, as if diametrically opposite to that where the of flames, was distinctly audible.” Burns, meteor appears, it seems probable that a good observer, if ever there was one, the aurora borealis is caused by the as- and not likely to be aware of any theocent of a considerable quantity of elec- ries on the subject, alludes in his “ Vistric fluid in the superior regions of the ion” to a noise accompanying the aurora, atmosphere to the north and northeast, as if it were of ordinary occurrence:where, consequently, it causes a body of

“ The cauld blue North was flashing forth air near the earth to ascend, when an

Her lights wi' hissing eerie din.” other current of air will rush from the the opposite point to fill up the vacuum, It finds confirmation also in the fact, and thus may produce the southerly gales generally admitted by the inhabitants which succeed the aurora borealis." of the northern regions, that, when the

The bark “ Northern Light,” arrived auroræ appear low, a crackling is heard at Boston from Africa, was at sea on similar to that of the electric spark. The the night of the great exhibition of the Greenlanders think that the souls of aurora borealis, the 28th of August. The the dead are then striking against each vessel was struck by lightning twice, after other in the air. M. Ramm, Inspector which the red flames of the aurora burst of Forests in Norway, wrote to M. Hanupon the astonished vision of the crew. steen, in 1825, that he had heard the Most of them are confident that they noise, which always coincided with the smelt a sulphurous odor all night. appearance of the luminous jets, when,

M. de Tessan, who, in the voyage of being only ten years old, he was crossthe “ Venus” around the world, had the ing a meadow covered with snow and opportunity of seeing a very beautiful hoar-frost, near which no forests were in aurora australis, (southern aurora,) which existence. Dr. Gisler, who for a long he describes with much care, also con- time dwelt in the North of Sweden, re siders that this phenomenon takes place marks that the matter of the auroræ boin the atmosphere. The summit of the reales sometimes descends so low that it aurora being in the magnetic meridi- touches the ground; at the summit of an, it was elevated 14° above the hori- high mountains it produces upon the zon, and the centre of the arc was on faces of travellers an effect analogous to the prolongation of the dipping needle, that of the wind. Dr. Gisler adds, that the dip being about 68° at the place of he has frequently heard the noise of the the observation. M. de Tessan did not aurora, and that it resembles that of a hear the noise arising from the aurora, strong wind, or the hissing that certain which he attributes to the circumstance chemical substances produce in the act that he was too far distant from the place of decomposition. of the phenomenon; but he reports the M. Necker, who has described a great observation of a distinguished officer of number of auroræ which he observed at the French navy, M. Verdier, who, on the end of 1839 and at the commencethe night of October 13th, 1819, being ment of 1840, in the Isle of Skye, nevin the latitude of Newfoundland, had er himself heard the noise in question ; heard very distinctly a sort of crackling but he remarks that this noise had been very frequently heard by persons charg- ter were powerfully magnetized, without, ed with meteorological observations at however, the apparatus being in action, the light-house of Swenburgh Head, at and without the currents in the battery the southern extremity of Shetland. M. being set in action. This singular effect Necker is not the only observer who has ceases with the aurora, and the telegraph, not heard the noise ; neither have MM. as well as the batteries, could operate Lottier and Bravais, who have observed anew, without having suffered any alteraso great a number of auroræ, ever heard tion. Mr. Highton also observed in Engit; and a great many others are in this land a very decided action of the aurora case. This


be due to the fact that borealis, November 17, 1848. The mag. it is necessary to be very near to the au- netized needle was always driven toward rora in order to hear the crepitation in the same side, even with much force. question, and also to the fact that it is But it is in our own country that the acpossible that it does not always take tion of the aurora upon the telegrapbplace, at least in a manner sufficiently wires has been the most remarkable. powerful to be heard.

My attention was first called in 1847 We have just been pointing out, as to the probability of the aurora's proconcomitant effects of the aurora bore- ducing an effect upon the wires; but, alalis, a noise of crepitation analogous to though having an excellent opportunity that of distant discharges, and a sulphur- to observe such an effect, I was not forous odor similar to that which accom- tunate enongh to do so until the winter panies the fall of lightning.' M. Mat- of 1850, and then, owing to the feeble teucci also observed at Pisa, during the displays of the aurora, only to a limited appearance of a brilliant aurora bore- extent. In September, 1851, however, alis, decided signs of positive electricity there was a remarkable aurora, which in the air ; but of all phenomena, those took complete possession of all the tele which invariably take place at the same graph-lines in New England and pretime as the appearance of the aurora bo- vented any business from being transrealis are the magnetic effects. Magne- acted during its continuance. The foltized needles suffer disturbances in their lowing winter there was another renormal direction which cause them to markable display, which occurred on the deviate generally to the west first, after- 19th of February, 1852. It was exceedwards to the east. These disturbances ingly brilliant throughout the northern vary in intensity, but they never fail to portion of our continent. I extract the take place, and are manifested even in following account of its effects upon the places in which the aurora borealis is not wires from my journal of that date. I visible. This coincidence, proved by M. should premise, that the system of teleArago without any exception, during sev- graphing used upon the wires, during the eral years of observation, is such that the observation of February, 1852, was Bain's learned Frenchman was able, without chemical. No batteries were kept conever having been mistaken, to detect stantly upon the line, as in the Morse and from the bottom of the cellars of the other magnetic systems. The main wire observatory of Paris the appearance of was connected directly with the chemicalan aurora borealis. M. Matteucci had ly prepared paper on the disc, so that the opportunity of observing this mag- any atmospheric currents were recordnetic influence under a new and re- ed upon the disc with the greatest accumarkable form. He saw, during the ap- racy. Our usual battery current, depearance of the aurora borealis of No- composing the salts in the paper, and vember 17, 1848, the soft iron armatures uniting with the iron point of the pen employed in the electric telegraph be- wire, left a light blue mark on the white tween Florence and Pisa remain attach- paper, or, if the current were strong, a ed to their electro-magnets, as if the lat- dark one,- the color of the mark depending upon the quantity of the cur- The wire between Boston and Fall rent upon the wire.

River had no battery upon it Sunday,

and yet there was an artificial current Thursday, February 19, 1852. upon it, which increased and decreased “ Towards evening a heavy blue line in intensity, producing upon the electroappeared upon the paper, which gradu- magnets in the offices the same effect as ally increased in size for the space of would be produced by constantly openhalf a minute, when a flame of fire suc- ing and closing the circuit at intervals ceeded to the blue line, of sufficient in- of half a minute. This current, which tensity to burn through a dozen thick- came from the aurora, was strong enough nesses of the inoistened paper. The cur

to have worked the line, although not rent then subsided as gradually as it had sufficiently steady for regular use. come on, until it entirely ceased, and was The current from the aurora borealis then succeeded by a negative current comes in waves, - light at first, then (which bleaches, instead of coloring, the stronger, until we have, frequently, a paper). This gradually increased, in the strength of current equal to that producsame manner as the positive current, un- ed by a battery of two hundred Grove til it also, in turn, produced its flame cups. The waves occupy about fifteen of fire, and burned through many thick- seconds each, ordinarily, but I have known nesses of the prepared paper; it then them to last a full minute ; though this is subsided, again to be followed by the rare. As soon as one wave passes, anpositive current This state of things other, of the reverse polarity, always succontinued during the entire evening, and ceeds. I have never known this to fail, effectually prevented any business being and it may be set down as an invariable done over the wires."

rule. When the poles of the aurora are

in unison with the poles of the current Never, however, since the establish- upon the line, its effect is to increase the ment of the telegraphic system in this current; but when they are opposed, the country, have the wires been so greatly current from the battery is neutralized, affected by the aurora as upon Sunday — null. These effects were observed at night, the 28th of August, 1859. Through- times during Saturday, Saturday evening, out the entire northern portion of the and Sunday, but were very marked durUnited States and Canada, the lines were ing Sunday evening. rendered useless for all business purposes It is hardly necessary to add here, that through its action. So strongly was the the effect of the aurora borealis, or magatmosphere charged with the electric flu- netic storm, is totally unlike that of comid, that lines or circuits of only twelve mon or free electricity, with which the miles in length were so seriously affected atmosphere is charged during a thunderby it as to render operation difficult, and, storm. The electricity evolved during a at times, impossible.

thunder-storm, as soon as it reaches a The effects of this magnetic storm were conductor, explodes with a spark, and apparent upon the wires during a consid- becomes at once dissipated. The other, erable portion of Saturday evening, and on the contrary, is of very low tension, during the whole of the next day. At 6, remains upon the wires sometimes half P. M., the line between Boston and New a minute, produces magnetism, decomBedford (sixty miles in length) could be poses chemicals, deflects the needle, and worked only at intervals, although, of is capable of being used for telegraphic course, no signs of the aurora were ap- purposes, although, of course, imperfectparent to the eye at that hour. The same ly. was true of the wires running eastward Mr. 0. S. Wood, Superintendent of through the State of Maine, as well as the Canadian telegraph-lines, says :those to the north.

“I never, in my experience of fifteen

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