AUROLITES. 117 



ever, than the mean density of the earth, they must he very 

 small nuclei, which, surrounded by inflammable vapor or gas, 

 form the innermost part of fire-balls, from the height and ap- 

 parent diameter of which we may, in the case of the largest, 

 estimate that the actual diameter varies from 500 to about 

 2800 feet. The largest meteoric masses as yet known are 

 those of Otumpa, in Chaco, and of Bahia, in Brazil, described 

 by Rubi de Celis as being from 7 to 7^ feet in length. The 

 meteoric stone of -i^gos Potamos, celebrated in antiquity, and 

 even mentioned in the Chronicle of the Parian Marbles, which 

 fell about the year in which Socrates was born, has been de- 

 scribed as of the size of two mill-stones, and equal in weight 

 to a full wagon load. Notwithstanding the failure that has 

 attended the efforts of the African traveler. Brown, I do not 

 wholly relinquish the hope that, even after the lapse of 2312 

 years, this Thracian meteoric mass, which it would be so dif- 

 ficult to destroy, may be found, since the region in which it 

 fell is now become so easy of access to European travelers. 

 The huge aerolite which in the beginning of the tenth centu- 

 ry fell into the river at Narni, projected between three and 

 four feet above the surface of the water, as we learn from a 

 document lately discovered by Pertz. It must be remarked 

 that these meteoric bodies, whether in ancient or modern times, 

 can only be regarded as the principal fragments of masses that 

 have been broken up by the explosion either of a fire-ball or 

 a dark cloud. 



On considering the enormous velocity with which, as has 

 been mathematically proved, meteoric stones reach the earth 

 from the extremest confines of the atmosphere, and the length- 

 ened course traversed by fire-balls through the denser strata 

 of the air, it seems more than improbable that these metallif- 

 erous stony masses, containing perfectly-formed crystals of oli- 

 vine, labradorite, and pyroxene, should in so short a period of 

 time have been converted from a vaporous condition to a solid 

 nucleus. Moreover, that which falls from meteoric masses, 

 even where the internal composition is chemically different, 

 exhibits almost always the peculiar character of a fragment, 

 being of a prismatic or truncated pyramidal form, with broad, 

 somewhat curved faces, and rounded angles. But whence 

 comes this form, which was first recognized by Schreiber as 

 characteristic of the severed part of a rotating planetary body \ 

 Here, as in the sphere of organic life, all that appertains to 

 the history of development remains hidden in obscurity. Me- 

 teoric masses become luminous and kindle at heights which 



