AEROLITES. 109 



shooting stars, there falls any compact substance, or only a 

 meteoric dust ( 61 ), containing iron and nickel., are questions 

 still wrapped in great obscurity. "We know, by measure- 

 ment,, the astonishing and wholly planetary velocity of shoot- 

 ing stars, fire-balls, and meteoric stones; in this respect, 

 therefore, we are able to recognise what is " general" and 

 " uniform" in the phsenomena ; but the genetic and cosmical 

 premises, the successive transformations undergone, are 

 not known to us. If meteoric stones circulate in space 

 in already consolidated and dense masses ( 62 ) (less dense, how- 

 ever, than the mean density of the earth), we must suppose 

 that they form very small nuclei, which, surrounded by in- 

 flammable vapours or gases, constitute fire-balls of from 500 

 to 2600 feet in actual diameter, as inferred in some of the 

 largest amongst them from observations of their height 

 and apparent diameter. The largest meteoric masses yei 

 known to us are those of Bahia in Brazil, and of Otumpa, 

 described by Rubin de Celis : these are seven and 

 seven and a half feet in length. The meteoric stone of 

 JEgos Potamos, celebrated in antiquity, and mentioned in 

 the Chronicle of the Parian Marbles, and which fell about 

 the year of the birth of Socrates, has been described as being 

 of the size of two millstones, and equal in weight to a full 

 waggon load. Notwithstanding the failure of the efforts of 

 the African traveller, Browne, I have not given up the hope 

 that this Thracian meteoric mass, which must have been so 

 difficult to destroy, may be found, after the lapse of more than 

 2300 years, by some of the European visitors to countries 

 which have now become so easy of access. We learn by a 

 document lately discovered by Pertz, that the enormous 

 aerolite wlu'ch, in the beginning of the tenth century, fell into 



