Curiosities of the Sky by Garrett Putman Serviss (good story books to read TXT) 📕

One of the first things recognized was the fact that fire-balls are solid meteorites in flight, and not gaseous exhalations in the air, as some had assumed. They burn in the air during their flight, and sometimes, perhaps, are entirely consumed before reaching the ground. Their velocity before entering the earth's atmosphere is equal to that of the planets in their orbits -- viz., from twenty to thirty miles per second -- a fact which proves that the sun is the seat of the central force governing them. Their burning in the air is not difficult to explain; it is the heat of friction which so quickly brings them to incandescence. Calculation shows that a body moving through the air at a velocity of about a mile per second will be brought, superficially, to the temperature of ``red heat'' by friction with the atmosphere. If its velocity is twenty miles per second the temperature will become thousands of degrees. This is the state of affairs with a meteorite rushing into the earth's atmosphere; its surface is liquefied within a few seconds after the friction begins to act, and the melted and vaporized portion of its mass is swept backward, forming the train of sparks that follows every great fire-ball. However, there is one phenomenon connected with the trains of meteorites which has never been satisfactorily explained: they often persist for long periods of time, drifting and turning with the wind, but not ceasing to glow with a phosphorescent luminosity. The question is, Whence comes this light? It must be light without heat, since the fine dust or vapor of which the train can only consist would not retain sufficient heat to render it luminous for so long a time. An extremely remarkable incident of this kind occurred on February 22, 1909, when an immense fire-ball that passed over southern England left a train that remained visible during two hours, assuming many curious shapes as it was drifted about by currents in the air.

But notwithstanding the enormous velocity with which meteorites enter the air they are soon slowed down to comparatively moderate speed, so that when they disappear they are usually traveling not faster than a mile a second. The courses of many have been traced by observers situated along their track at various points, and thus a knowledge has been obtained of their height above the ground during their flight and of the length of their visible courses. They generally appear at an elevation of eighty or a hundred miles, and are seldom visible after having descended to within five miles of the ground, unless the observer happens to be near the striking-point, when he may actually witness the fall. Frequently they burst while high in the air and their fragments are scattered like shrapnel over the surface of the ground, sometimes covering an area of several square miles, but of course not thickly; different fragments of the same meteorite may reach the ground at points several miles apart. The observed length of their courses in the atmosphere varies from fifty to five hundred miles. If they continued a long time in flight after entering the air, even the largest of them would probably be consumed to the last scrap, but their fiery career is so short on account of their great speed that the heat does not have time to penetrate very deeply, and some that have been picked up immediately after their fall have been found cold as ice within. Their size after reaching the ground is variable within wide limits; some are known which weigh several tons, but the great majority weigh only a few pounds and many only a few ounces.

Meteorites are of two kinds: stony meteorites and iron meteorites. The former outnumber the latter twenty to one; but many stone meteorites contain grains of iron. Nickel is commonly found in iron meteorites, so that it might be said that that redoubtable alloy nickel-steel is of cosmical invention. Some twenty-five chemical elements have been found in meteorites, including carbon and the ``sun-metal,'' helium. The presence of the latter is certainly highly suggestive in connection with the question of the origin of meteorites. The iron meteorites, besides metallic iron and nickel, of which they are almost entirely composed, contain hydrogen, helium, and carbonic oxide, and about the only imaginable way in which these gases could have become absorbed in the iron would be through the immersion of the latter while in a molten or vaporized state in a hot and dense atmosphere composed of them, a condition which we know to exist only in the envelopes of the sun and the stars.

The existence of carbon in the Canyon Diablo iron meteorites is attended by a circumstance of the most singular character -- a very ``fairy tale of science.'' In some cases the carbon has become diamond! These meteoric diamonds are very small; nevertheless, they are true diamonds, resembling in many ways the little black gems produced by Moissan's method with the aid of the electric furnace. The fact that they are found embedded in these iron meteorites is another argument in favor of the hypothesis of the solar or stellar origin of the latter. To appreciate this it is necessary to recall the way in which Moissan made his diamonds. It was by a combination of the effects of great heat, great pressure, and sudden or rapid superficial cooling on a mass of iron containing carbon. When he finally broke open his iron he found it a pudding stuffed with miniature black diamonds. When a fragment of the Canyon Diablo meteoric iron was polished in Philadelphia over fifteen years ago it cut the emery-wheel to pieces, and examination showed that the damage had been effected by microscopic diamonds peppered through the mass. How were those diamonds formed? If the sun or Sirius was the laboratory that prepared them, we can get a glimpse at the process of their formation. There is plenty of heat, plenty of pressure, and an abundance of vaporized iron in the sun and the stars. When a great solar eruption takes place, masses of iron which have absorbed carbon may be shot out with a velocity which forbids their return. Plunged into the frightful cold of space, their surfaces are quickly cooled, as Moissan cooled his prepared iron by throwing it into water, and thus the requisite stress is set up within, and, as the iron solidifies, the included carbon crystallizes into diamonds. Whether this explanation has a germ of truth in it or not, at any rate it is evident that iron meteorites were not created in the form in which they come to us; they must once have been parts of immeasurably more massive bodies than themselves.

The fall of meteorites offers an appreciable, though numerically insignificant, peril to the inhabitants of the earth. Historical records show perhaps three or four instances of people being killed by these bodies. But for the protection afforded by the atmosphere, which acts as a very effective shield, the danger would doubtless be very much greater. In the absence of an atmosphere not only would more meteorites reach the ground, but their striking force would be incomparably greater, since, as we have seen, the larger part of their original velocity is destroyed by the resistance of the air. A meteorite weighing many tons and striking the earth with a velocity of twenty or thirty miles per second, would probably cause frightful havoc.

It is a singular fact that recent investigations seem to have proved that an event of this kind actually happened in North America -- perhaps not longer than a thousand or two thousand years ago. The scene of the supposed catastrophe is in northern central Arizona, at Coon Butte, where there is a nearly circular crater in the middle of a circular elevation or small mountain. The crater is somewhat over four thousand feet in diameter, and the surrounding rim, formed of upturned strata and ejected rock fragments, rises at its highest point one hundred and sixty feet above the plain. The crater is about six hundred feet in depth -- that is, from the rim to the visible floor or bottom of the crater. There is no evidence that volcanic action has ever taken place in the immediate neighborhood of Coon Butte. The rock in which the crater has been made is composed of horizontal sandstone and limestone strata. Between three hundred and four hundred million tons of rock fragments have been detached, and a large portion hurled by some cause out of the crater. These fragments lie concentrically distributed around the crater, and in large measure form the elevation known as Coon Butte. The region has been famous for nearly twenty years on account of the masses of meteoric iron found scattered about and known as the ``Canyon Diablo'' meteorites. It was one of these masses, which consist of nickel-iron containing a small quantity of platinum, and of which in all some ten tons have been recovered for sale to the various collectors throughout the world, that as before mentioned destroyed the grinding-tool