. Guide leaflet. morefrequently than theiron meteorites, ofwhich 350 had beenfound to 1929, butonly 22 seen to number of fallsand finds known in1929 was 832. Thelist has been consid-erably increased dur-ing the following fouryears. The AmericanMuseum Collectionof meteorites (March,1933) contained 2640specimens, represent-ing 569 falls and collectionsof meteorites reveal that the specimens of no two falls areexactly alike in structure or composition,yet it has been observed that they may bearranged into three principal groups orkinds, as noted by MerriU namely: 1. Aerolites
. Guide leaflet. morefrequently than theiron meteorites, ofwhich 350 had beenfound to 1929, butonly 22 seen to number of fallsand finds known in1929 was 832. Thelist has been consid-erably increased dur-ing the following fouryears. The AmericanMuseum Collectionof meteorites (March,1933) contained 2640specimens, represent-ing 569 falls and collectionsof meteorites reveal that the specimens of no two falls areexactly alike in structure or composition,yet it has been observed that they may bearranged into three principal groups orkinds, as noted by MerriU namely: 1. Aerolites, or stony meteorites, consisting essentially of silicate minerals with minoramounts of the metallic alloys andsulphides. 2. Siderolites or stony-iron meteorites, con- sisting of an extremely variable networkor sponge of metal, the interstices ofwhich are occupied by one or moresilicate minerals. 3. Siderites or iron meteorites, consisting essentially of an alloy of nickel-ironwith iron phosphides and Technical students of meteorites havesubdivided each of these groups. Theaerolites and siderites are, however, themore common kinds. When cut, pol-ished and etched, the siderites, or ironmeteorites, usually show peculiar mark-ings of crossed lines, and thus can beeasily distinguished from the terrestrialirons. Some siderites have the nickel-ironalloys arranged in the form of platesparallel with the faces of an lamellae may be of different degreesof thickness and composed of one, two orthree kinds of metal. On etching withacid these metallic bands react unequally 16 NATURAL HISTORY and show characteristic figures known asWidnianstatten hnos. Another group of iron meteorites, com-posed of homogeneous masses of nickel-iron, show cleavage and lamellae parallelto the faces of a hexahedron. This is due tothe twinning of a cube on an octahedralface. On etching with dilute nitric acidthe structures show Neumann lines. Suchforms are known as hexahedral irons. A
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectnatural, bookyear1901
