126 



veniently arranged in three groups, which pass more or less- 

 gradually into each other : the first includes all those which 

 consist mainly of iron, and have, therefore, been called aerosi- 

 derites (sky-irons), or, more shortly, siderites ; the second is 

 formed by those which are composed of iron and stone, both 

 in large quantity, and are called aerosiderolites (sky-iron- 

 stones), or, shortly, siderolites ; while those of the last group,, 

 being almost wholly of stone, are called aerolites (sky-stones). 



Tn the aerosiderites the iron generally varies from 80 to 

 95 per cent., the nickel from 6 to 10 per cent. ; in the Mom> 

 do Ricio iron (109 J) 34, and in that of Oktibbeha County 

 (64 G) as much as 60 per cent, of nickel have been found: the 

 nickel is in part at least alloyed with iron, and several of 

 these alloys have been distinguished by special names. There 

 are also frequently present troilite in veins or large nodules r 

 sometimes surrounded by graphite, carbon in combination 

 with the iron, and also schreibersite and daubreelite. Further,, 

 the researches of Berzelius, Boussingault, Graham and Mallet 

 have proved the presence of the gases hydrogen, nitrogen and 

 the carbonic oxides occluded in the iron ; Dr. Walter Flight 

 has lately shown that the gases occluded in the Row ton iron 

 (110 J) would under normal temperature and pressure have 

 a volume upwards of six times that of the meteorite itself. 

 The want of homogeneity in meteoric iron is beautifully 

 shown by the ' Widmanstatten ' figures called into existence 

 when a polished surface is exposed to the action of acids or 

 bromine ; they are due to the unequal action on the various 

 constituents, and are formed by layers of schreibersite and of 

 tsenite, one of the alloys of nickel and iron ; see Zacatecas 

 (6 B), Lockport (14 C) and Seneca River (49 E). 



The aerosiderites actually observed to fall reach only the 

 small number of six ; they are, Agram (B 1 ), Charlotte 

 (27 D), Braunau (43 E), Tabarz (60 F), Nedagolla (106 J), 

 and Rowton (110 J) ; besides these, there are two others, of 

 which the dates of fall are doubtful. The remaining specimens 

 in collections of aerosiderites are presumed to be of meteoric 

 origin by reason of their peculiar appearance and composition, 

 and of circumstances connected w T ith the locality in which they 

 have been found. The difficulty of distinguishing an iron of 



