A TALK ABOUT METEORITES. 373 



out during a slow process of crystallization, evidently from a 

 melted condition. This structure is best seen on a polished sur- 

 face which has been subject to tempering, or else etched with 

 acid. The acid, acting most readily upon the purest parts of 

 the iron, develops certain figures called Widmanstattian figures 

 if the plates are broad and well marked, and called Neumann 

 lines where they are reduced to fine markings. Till recently, 

 these two varieties of etched figures were supposed to indicate a 

 difference of crystalline structure ; but, by a study of the Harvard 

 collection (American Journal of Science, third series, vol. xxxii, 

 p. 284), it has been shown to depend on the time of crystallization 

 — that is to say, on merely the size of the crystals, and not a differ- 

 ence of form. In some cases these etched figures serve conclu- 

 sively to distinguish irons of different falls, but frequently they 

 vary on the same specimen, or depend on the direction in which 

 the surface is cut ; but there are large groups of irons closely re- 

 sembling each other in their etched characters. The distinction 

 of such irons has become of great importance, since the enormous 

 prices paid for meteorites offers a strong inducement to multiply 

 supposed falls. Iron meteorites are often cut up and distributed 

 by the finders before they have been fully identified, and the con- 

 fusion is further increased by the natural distribution due to the 

 explosions in the upper atmosphere. Thus a meteorite which fell 

 in Cocke County, Tennessee, some time previous to 1840, has been 

 turning up at various places ever since, and the numerous frag- 

 ments have been described from time to time under various names 

 as different falls. 



In an attempt to prove that an iron which was found in Mav- 

 erick County, Kentucky, was identical with two Mexican ones, in 

 the Harvard collection (Proceedings of the American Academy of 

 Arts and Sciences, vol. xxiv, p. 30), the writer found that on break- 

 ing slabs of the respective irons the two Mexican specimens, which 

 had been generally accepted as identical, showed a marked differ- 

 ence of structure. One of them, known as the Butcher iron, when 

 broken in various directions by blows of a hammer, always exhib- 

 ited most brilliant and complex crystal faces, some of them half 

 an inch in diameter, certain of the faces being most beautifully 

 marked by a system of fine parallel lines arranged at certain fixed 

 angles. The second iron, on the other hand, from Santa Kosa, would 

 only break in two definite directions, exhibiting a single face with 

 little flaky surfaces, but none of the fine lines. This last iron, if 

 sawed to a thin edge, and then forced to break in a different direc- 

 tion from the two just mentioned, showed only a series of little 

 cube faces, very different from the Butcher iron. 



On a similar examination of other irons resembling the two 

 Mexican ones in the figures brought out by etching, irons from 



