Hraschina fireball and smoke trails. Photo credit: WikiCommons/kork

 

The fall at Hraschina on May 26, 1751, is scientifically important for two main reasons.

Firstly, it was the first documented, observed fall of an iron meteorite. Secondly, when the material was analysed, under heating it revealed hints of the Widmannstatten patterns which are nowadays revealed by etching with acid. At the time, the scientists analysing it believed this was the first time these had been observed  *.

Here is a report of a presentation given by Professor Haidinger, who also illustrated the beautiful picture to the left. (Source: Reports of the BAAS, 1861, p32 et seq):

One of the most interesting falls of meteorites, and for a long time the only one of metallic iron which had been witnessed, took place at Hraschina, near Agram, on May 26th 1751. At a meeting of the Imperial Academy of Vienna, April 14th, 1859, M Haidinger produced the Latin document referring to it (which had never been published), and the original German translation; also a second document, lately discovered in the Imperial Cabinet of Minerals in Vienna, accompanied by two plates representing the phenomena as observed at Szigetvar (or Gross-Sziget), 75 miles east of Hraschina. At a meeting held on Friday 3rd, 1860, he presented a third document, discovered in the archiepiscopal library at Agram, describing the same phenomena as seen at Biscupez, near Warasdin, 17.5 miles north, a little east of Hraschina.

Prof Haidinger also drew attention to the meteor seen on May 26, 1751, between 6 and 7pm, west of Gross-Sziget. It was first observed as a flash of light, without noise; immediately afterwards it resembled a tortuous chain, extending directly west, terminating in the middle height of the air as a fireball, leaving a long trail. On arriving at the lower strata it resembled an enormous sparkling fireball, with a chain-like tail in the higher regions, the last traces of which faded away about 10pm. At Biscupez it was observed as a small cloud from which some noise emanated, and which afterwards disappeared.

Two pieces of iron fell to the east of Hraschina, one of 71lbs penetrating 4 feet 6 inches into the ground, at present preserved in the Imperial Cabinet of Vienna; the other of 16lbs, which had been distributed partly at the place of its fall, and afterwards at Presburg, every vestige of which is lost. From the computations of various observations it appears to have passed from Neustadt to Hraschina, or from north to south from 48º 35′ to 40º 6′ 2″; and from west to east from 28º 18′ to 34º, east of Ferro.

No observations were taken of its velocity; but its height before its fall at Hraschina, viewed from Szigetvar, was from 30º to 35º – equal to about 43 to 52.5 miles. Prof Haidinger remarked upon the vast difference between the apparent size of the meteor and its solid contents. A body 15 inches in diameter at 75 miles distance is invisible; yet the meteor is pictured as if of the size of the sun. The appearance of the chain indicates the time when the solid portions became visible; they are, however, only the paths of the luminous bodies; and that they do not form straight lines is very natural, if we take into consideration the flat shape of the meteorite, which must have been tossed from side to side by the resistance of the air. If the rapid compression of the air is sufficient to annul the cosmic velocity, it certainly can produce the elimination of light – the fiery phenomena.

These two points established, as a natural consequence two phenomena result, which belong to the character of fiery meteors. The solid nucleus of a meteor is not a globe; it passes undoubtedly through the resisting medium with its centre of gravity foremost, producing, on account of the unequal distribution, a rotation of its mass, which increases in rapidity, whilst the velocity of its motion diminishes in direct ratio.

The report of the Hraschina meteor was heard as far as Warasdin, which, taking Hraschina as a centre, gives an area of nearly 1,000 square miles over which the sound was audible

The Hraschina iron was the first in which the highly crystalline structure of meteoric iron was observed, and Haidinger gives us an account of  the circumstances under which the discovery was made. Alvis von Widmannstatten, a highly educated and thorough iron-master, had a plate of the mass cut off 1.75 by 1 inch in size and 3/16 oz in weight; this was carefuly polished for the purpose of examination when exposed to heat.

But what a surprise! After the colour of the principle mass has passed through the various shades of straw-yellow, brownish-yellow, violet and blue, there remained groups of triangles of straw-colour parallel lines, the blue and violet intervals 1/4 to 1/2 line wide, the straw-yellow ones 1/6 to 1/4 – a splendid phenomenon. This was the first observation, and the figures were called ‘Widmanstatten’s figures’ in honour of the discoverer. The method of etching by acids was introduced after this discovery.*

 

Here is a second report form the American Journal of Science and Arts, Volume 15 (1826):

Hraschina. Photo credit WikiCommons/saperaud

This most interesting meteorite, which fell May 26, 1751, and for nearly 100 years was the only one of the metallic class positively known to have fallen from the heavens, was first seen as a brilliant fireball passing from west to east through a cloudless sky at 6pm, attended with a noise like that produced by heavy wagons rapidly passing over a paved road. When almost directly over the village of Hraschina, it burst with a tremendous explosion into two pieces, and at the same moment became enveloped in a cloud of smoke, which was at first black, and then presented a variety of colors. The fall was followed by a terrible crash, and a trembling as from an earthquake.

The larger fragment, which weighed 71lbs (Austrian) made an opening in the earth 18 feet deep and 2 feet wide, while the smaller of 16lbs weight buried itself in a meadow 2000 paces distant. The large mass was presented to the Emperor Francis I, and the Empress, Maria Theresa, by the bishop of Agram, and is preserved in the Imperial Museum in Vienna. The smaller mass is missing.

The mass has a triangular, tabular form, with one side convex and other slightly concave. It has a complete crust, in which is enclosed no gravel or earthy matter, as must have been the case had it been in a liquid condition. It undoubtedly came to the earth in a glowing state, and revolving rapidly like a circular saw, so as to strike the ground edgewise, and thus penetrate to such an astonishing depth. The surface presents the usual concavities. The crust is brownish-black and without lustre, with a thickness of about three-fourths of a line, though varying on different parts.

It is somewhat fibrous in structure, and readily separated from the metal beneath, which then appears smooth and polished. On the convex side of the mass, the crust contains numerous fissures, usually about one-half inch long, though rarely from one to two inches, and from two-twelfths to three-twelfths of a line deep. The mass contains occasional intermixtures of magnetic pyrites, and displayed on fractured surfaces a crystalline structure.

When etched, it exhibits most perfectly those characteristic figures which were first discovered in this iron, by Widmannstatt in Vienna in 1808.*

 

* Note that, as far as the original authors were concerned, they were accurately reporting the fact that Widmannstatten was the first to observe the famous patterns. However, more recent research has shown that they were, in fact, independently discovered four years earlier by the English geologist G Thomson. Indeed, his discovery (after attempting to clean the Krasnojarsk meteorite with nitric acid), unlike Widmannstatten’s, was actually published – in 1804. Thomson should thus be awarded credit through both prior discovery and publication.

The term ‘Widmannstatten pattern’ appears to have stuck, although some (O Richard Norton among them) have suggested the term ‘Thomson structure’. Either are acceptable.

(Thanks to Mike Bandli for pointing out the error in the original version of this page, and for permission to link to his page on Thomson).