David Forhes-^On Meteorites. 229 



of country as large as Great Britain and Prance united, an estimate 

 which is probably under the trutli.- 



Turning now to the chemical and mineralogical composition of 

 meteorites, it may be premised that, in these respects, they are so 

 distinct from any known terrestrial product as not to lead to any 

 risk of their being confounded with such, and also that meteoric 

 stones pertaining to each of the three different classes of meteorites 

 about to be m'entioned possess a wonderful resemblance to one 

 another, quite irrespective of the part of the world they may come 

 from. 



The three classes into which meteorites are divided are called — 



Aerolites- proper; i.e. atmospheric stones or rocks ; 



Siderites, or masses of meteoric iron ; and 



Siderolites, which are a mixture of both the former. 



The stones of all these classes are, upon touching the earth, found 

 to be extremely hot, and the more so in proportion as they are good 

 conductors. The siderites which fell at Agram were almost on the 

 point of fusion ; whilst aerolites have sometimes been found semi- 

 plastic, so as to receive impressions from or even entangle substances 

 on which they have fallen ; the sole exception we know of being that 

 of a stone which fell at Dhurmsalla in the Punjaub, which the coolies 

 who picked it up declared to have been so cold as to benumb their 

 fingers and make them instantly drop it, — a statement strangely at 

 variance with the vitreous black glaze on its exterior, due to the 

 rapid fusion of its exterior in its passage through the air — and the 

 whole reminds us of the celebrated Chinese delicacy " baked ice." 

 This black glaze, or varnish as it is sometimes called, is so character- 

 istic of aerolites, that only one exeeption is known (from Chanton- 

 nay). It is usually so thin as not to attain the thickness of an egg- 

 shell, and frequently covers the exterior of stones, which, from their 

 shape, are evidently only fragments of larger masses, so that it must 

 have formed after the explosion which shattered the parent mass ; 

 and here it may be remarked, that aerolites when foimd are rarely 

 entire; thus for example, at Gurucpoor, in 1861, stones obtained, after 

 the explosion of the meteor, miles apart, were found to fit into one 

 another, and had evidently formed part of one large mass. 



Mineralogically, the siderites or metallic meteorites consist mainly 

 of an alloy of iron with from one to fifteen per cent, of nickel, — an 

 alloy altogether different in chemical composition and physical 

 structure from any known product of terrestrial origin, whether 

 natural or artificial. This nickeliferous iron, owing to its being less 

 oxidizable than pure iron, is capable of resisting atmospheric in- 

 fluences for periods in which similar masses of ordinary iron would 

 have rusted away into powder ; and it is mainly for this reason, in 

 conjunction with its superior toughness, which prevents its being 

 easily broken in its descent to the earth as aerolites do, that most of 

 the largest metorites now known belong to the class of siderites — as, 

 for example, one at Bahia in Brazil, weighing nearly 7 tons ; another 

 in the Chaco, also in South America, estimated at 13 tons : and the 

 largest of all the known meteorites, which a few months ago was 



