on the horizon of a brown haze, passing into violet, through which the stars may be dimly seen, which is diffused laterally and upward to a height of from 5° to 10°, at which it is bounded by a luminous arc. This is occasionally agitated for hours by a tremulous movement and seeming effervescence ere rays of light rush from it upward into the zenith, glowing with the prismatic colours between violet and purple red, whose rapid undulatory motion causes a continuous change in their form and splendour. Sometimes these columns of light are mingled with dark rays, somewhat like Fraunhofer’s lines in the solar spectrum; at others the whole heaven is radiant with coruscations, whose brilliancy seems intensified by the rapidity of their emission, though it is ever greatest at the arc in which they originate. When these streams of glory, rising simultaneously from various points, unite in the zenith, they form a brilliant crown of light; but this is rare, and always premonitory of the end of the aurora, which then rapidly pales and vanishes, leaving as records of its presence only a faint haze on the horizon, and a few nebulous spots arranged in streaks upon the sky. A faint sulphurous odour is at times apprehended, similar to that attendant on a thunderstorm, and a sharp crepitation has been heard, regarding which the incredulity of some in opposition to reliable testimonies is not very philosophical. Burns, who was a good observer of nature, alluded to it, and his evidence is not to be despised:
“The cauld blue North was flashing forth
Her lights wi’ hissing eerie din—”
Signs of positive electricity have also been frequently observed in the atmosphere at these times.
It has been observed that auroras are most vivid and frequent when the higher atmosphere contains those delicate flowing clouds, termed cirri. These have a singular tendency to Polar arrangement, like that of the auroral rays, and occasionally a train of cirri thus disposed have been identified as having been luminous rays the preceding night,—the vehicle of an evanescent splendour.
The condition of the atmosphere, indicated by cirri, is attended with magnetic disturbances. This having been stated, the coincidence of cirri with auroras gives a special significance to their meridional direction and evolution of light at the Poles, did those facts stand alone. But of all phenomena accompanying the aurora those most invariable are magnetic ones. The needle is deflected by it first west, then east. This is noticed even in distant places where the aurora is not visible, proving that the action is not merely local; and so invariable are these magnetic disturbances, that the celebrated Arago was thereby enabled to detect the presence of an aurora from the subterranean chambers of the Paris observatory.
But the most remarkable evidence of the immediate presence of the aurora is its influence on telegraphic lines, consisting not merely in a momentary interruption of communication like that occurring during a thunder-storm, but in the magnetic action on the magnets and actual occupation of the wires. These strange phenomena vary with the intensity of the aurora, but they have been satisfactorily determined by repeated observation, all telegraphic operations being sometimes stopped for hours.
To apprehend clearly the nature of this auroral action on the wires as distinguished from that of a thunderstorm, it must be premised that the voltaic or chemical electricity used for telegraphic purposes is of low tension, continuous flow, and perfectly controllable; whereas the free electricity of the atmosphere is of high tension, exploding with vivid light when it finds a conductor, and “dying in the very moment of its birth.” During a vivid aurora a new mode of electricity, of totally distinct character from either of these, is revealed: it has low tension, chemical decomposing power, alternating polarity, induces magnetism, and produces on the electro-magnets of a line the same effect as that of continuously opening and closing the circuit. An instance of this specific action may be adduced.
In 1852, when auroras were very brilliant throughout North America, the auroral current manifested itself unmistakeably on many of the telegraphic lines. The main wire of one particular line, to which we have reference, was connected with a chemically prepared paper on a disk, and on this the ordinary atmospheric currents were actually self-registered. The usual voltaic current—decomposing the salts of the paper and uniting with the iron point of the pen—left a blue mark varying with the intensity of its action. On this occasion, the batteries being at the time detached, a dark blue line appeared on the moistened paper, and was succeeded by an intense flame which burnt through twelve thicknesses. This current then gradually died away, and was followed by a negative one which bleached and changed similarly into flame. The force which had thus intervened on the wires continued to act as long as the aurora lasted, and effectually put a stop to business.
Extraordinary as it may seem, the auroral current—the presence of which has been thus made visible—has been actually used for the transmission of human thought very recently.
The brilliant auroras of last autumn, which excited the admiration of England, while interrupting its means of communication, were not merely local, but prevailed simultaneously all over Europe, Northern Africa, Northern America, the West Indies, and Australia, satisfactorily establishing the unity of the action. This magnetic or auroral storm had rendered all the telegraphic lines of Canada and the Northern States unavailable, except at irregular intervals, for several days.
On the 2nd of September, the auroral influence being very active in the Boston terminus of the Boston and Portland line, the proper voltaic current being alternately intensified and neutralised by it visibly, it occurred to the interested operator in the office, that if the batteries were detached from the line, and the wires connected with the earth, the intruding auroral current might, perchance, be made use of. The idea is characteristically American in its utilitarianism. Having