The wonders of the world

by John Loraine Abbott

CONCENTRIC RAINBOWS.

This extraordinary phenomenon, which is seen at sunrise on the Andes, in South America, was first witnessed by Ulloa and his companions in the wild heaths of Pambamarca, and is thus described by him. “At day-break the whole of the mountain was enveloped in dense clouds, which at sunrise were dissipated, leaving behind them vapors of so extreme a tenuity, as not to be distinguishable to the sight. At the side opposite to that where the sun rose on the mountain, and at the distance of about sixty yards from the spot where we were standing, the image of each of us was seen represented as if in a mirror, and three concentric rainbows, the last or most exterior colors of one of which touched the first of the following one, were centered on each head. Without the whole of them, and at an inconsiderable distance, was seen a fourth arc purely white. They were all perpendicular to the horizon; and in proportion as any one of us moved from one side to the other, he was accompanied by the phenomenon, which preserved the same order and disposition. What was, however, most remarkable, was this, that although six or seven persons were thus standing close together, each of us saw the phenomenon as it regarded himself, but did not perceive it in the others. This, adds Bouguer, is a kind of apotheosis, in which each of the spectators, seeing his head adorned with a glory formed of three or four concentric crowns of a very vivid color, each of them presenting varieties similar to those of the first rainbow, tranquilly enjoys the sensible pleasure of reflecting that the brilliant garland he can not discover in the others is destined for himself alone.”

A similar phenomenon is described by Mr. Hagarth, as having been seen by him in Wales, on the thirteenth of February, 1780. His relation is as follows. “In ascending, at Rhealt, the mountain which forms the eastern boundary of the vale of Clwyd, (in Denbighshire,) I observed a rare and curious phenomenon. In the road above me, I was struck with the peculiar appearance of a very white, shining cloud, which lay remarkably close to the ground. The sun was near setting, but shone extremely bright: I walked up to the cloud, and my shadow was projected into it, its superior part being surrounded, at some distance, by a circle of various colors, whose center appeared to be near the situation of the eye, and whose circumference extended to the shoulders. This circle was complete, except what the shadow of my body intercepted. It exhibited the most vivid colors, the red being outermost; and all of them appearing in the same order and proportion as they are presented to the view by the rainbow. It resembled very exactly what in pictures is termed a glory, surrounding the heads of saints; not indeed that it exhibited the luminous radiance that is painted close to the head, but an arch of concentric colors placed separately and distinctly from it. As I walked forward, this glory approached or retired, just as the inequality of the ground shortened or lengthened my shadow. The cloud being sometimes in a small valley below me, sometimes on the same level, or on higher ground, the variation of the shadow and glory became extremely striking and singular. To add to the beauty of the scene, there appeared, at a considerable distance to the right and left, the arches of a white, shining bow. These arches were in the form of, and broader than a rainbow; but were not completely joined into a semicircle above, on account of the shallowness of the cloud.”

THUNDER AND LIGHTNING.

To conceive justly of the nature of thunder and lightning, we have only to view the effects of a common electrical machine, and its apparatus, in an apartment. These experiments mimic the great, wonderful and terrific phenomena of nature. The stream, or spark, from the machine to the hand, represents the shaft of lightning from the clouds to the earth; and the snapping noise of the diminutive spark corresponds with the explosion produced by the lightning, which we call thunder. In what manner the clouds become electrified, and, in short, what is the nature of electricity itself, our present range of experiments so little qualify us to determine, that a century will perhaps elapse before a philosophical precision can be attained. At present we only know for certain that the electrical power displays itself merely on the surface of bodies; and whether it is a fluid per se, a vacuum restoring itself, or whatever its nature may be, the state of experimental knowledge does not enable us to determine.

The obvious analogy between lightning and electricity, had long been suspected, and was placed beyond a doubt by Franklin, who was the first to conceive the practicability of drawing down lightning from the clouds. Having found by previous experiments, that the electric fluid is attracted by points, he apprehended that lightning might likewise possess the same quality; although the effects of the latter would in that case surpass those of the former in an astonishing degree. Flashes of lightning, he likewise observed, are generally seen crooked and waving in the air; and the electric spark drawn from an irregular body at some distance, when it is drawn by an irregular body, or through a space in which the best conductors are disposed in an irregular manner, always exhibits the same appearance.

Lightning strikes the highest and most pointed objects in its way, in preference to others, as high hills, trees, spires, masts, &c.; and all pointed conductors receive and throw off the electric fluid more readily than those which are terminated by flat surfaces. Lightning is observed to take the best and readiest conductor; and this is also the case with electricity, in the discharge of the Leyden phial; whence Franklin inferred that, in a thunder-storm, it would be safer for a person to have his clothes wet than dry. Lightning burns, dissolves metals, rends some particular bodies, such as the roots and branches of trees, strikes persons with blindness, destroys animal life, deprives magnets of their virtue and reverses their poles; and these are well known properties of electricity. Lightning not only gives polarity to the magnetic needle, but to all bodies which have any portion of iron in them, as brick, &c.; and, by observing which way the poles of these bodies lie, the direction in which the stroke has passed may be known with the utmost certainty.

In order to demonstrate, by actual experiment, the identity of the electric fluid with the matter of lightning, Franklin contrived to bring lightning from the heavens by means of an electrical kite, which he raised on the approach of a thunder-storm; and, with the electricity thus obtained, charged phials, kindled spirits, and performed all other electrical experiments, as they are usually exhibited by an excited globe or tube. This happened in 1752, a month after the French electricians, pursuing the method which he had proposed, had verified the same theory; but without any knowledge on his part of what they had done. On the following year, he further discovered that the air is sometimes electrified positively, and sometimes negatively; and that in the course of one thunder-storm, the clouds change from positive to negative electricity several times. He was not long in perceiving that this important discovery was capable of being applied to practical use; and proposed a method, which he soon accomplished, of securing buildings from being damaged by lightning, by means of conductors, or lightning-rods, the use of which is now universally known.

From a number of judicious experiments made by him, Signor Beccaria concluded that the clouds serve as conductors to convey the electric fluid from those parts of the earth which are overloaded with it, to those where it is exhausted. The same cause by which a cloud is first raised, from vapors dispersed in atmosphere, draws to it those which are already formed, and still continues to form new ones, till the whole collected mass extends so far as to reach a part of the earth where there is a deficiency of the electric fluid, and where the electric matter will discharge itself on the earth. A channel of communication being thus produced, a fresh supply of electric matter is raised from the overloaded part, which continues to be conveyed by the medium of the clouds, till the equilibrium of the fluid is restored between the two places of the earth. He further observes that as the wind constantly blows from the place where the thunder-cloud proceeds, the sudden accumulation of such a prodigious quantity of vapors must displace the air, and repel it on all sides. Indeed, many observations of the descent of lightning confirm his theory of the mode of its ascent; for it often throws before it the parts of conducting bodies, and distributes them along the resisting medium through which it must force its passage; and on this principle the longest flashes of lightning seem to be produced, by its forcing in its way part of the vapors in the air. One of the chief reasons why the report of these flashes is so much protracted, is the vast length of the vacuum made by the passage of the electric matter; for although the air collapses the moment after it has passed, and the vibration, on which the sound depends, commences at the same moment, still, when the flash is directed toward the person who hears the report, the vibrations excited at the nearer end of the track will reach his ear much sooner than those from the remote end, and the sound will, without any echo or repercussion, continue till all the vibrations have successively reached him. The rattling noise of the thunder, which makes it seem as if it passed through arches or were variously broken, is probably owing to the sound being excited among clouds hanging over one another, and the agitated air passing irregularly between them.

Among other precautions pointed out by Franklin, he recommends to those who happen to be in the fields, at the time of a thunder-storm, to place themselves within a few yards of a tree, but not quite near it. Signor Beccaria, however, cautions persons not to depend on a higher, or, in all cases, a better conductor than their own body; since, according to his repeated observations, the lightning by no means descends in one undivided track, but bodies of various kinds conduct their share of it at the same time, in proportion to their quantity and conducting power. The late Earl of Stanhope, in his principles of electricity, observes that damage may be done by lightning, not only by the main stroke and lateral explosion, but likewise by what he calls the returning stroke; that is, by the sudden violent return of that part of the natural share of electricity of any conducting body, or any combination of conducting bodies, which had been gradually expelled from such body or bodies respectively, by the superinduced elastic electrical pressure of a thunder-cloud’s electrical atmospheres.