﻿and Acoustic Phenomena attending the Fall of Meteorites. 257 



ference of internal and external expansive tension ; the fragments 

 thrown out in every direction pursue their course through cos- 

 mical space. 



The effective formation of the mass of meteorites falls entirely 

 within the third period ; it can, however, only proceed very 

 gradually. At the moment of a destructive catastrophe many 

 substances, different in nature or in progress of evolution, may 

 coexist, all of them, however, impressed with a common cha- 

 racter. Soft or hard meteorites, non-crystalline and more or 

 less distinctly crystallized ones, bear the mark of more or less 

 advanced evolution ; all of them, however, show a distinct 

 tufaceous structure and a breccia-like formation, the meteoric 

 iron, partly eminently crystalline, representing veins included in 

 a more solid matrix. Traces of gradual formation occur every- 

 where ; nor do the meteorites of Orgueil prove an exception to 

 this rule. Although composed of substances of rarer occurrence, 

 they show the general tufaceous type. Professor Daubree says 

 (p. 3), "They [the common meteorites] seem indeed to have 

 been formed at once ; it seems this was not the case with the 

 mass of which the Orgueil meteorites are fragments." And, 

 speaking of the common meteorites, he says (p. 4), " whose ge- 

 neral character is to be capable of being produced via sicca 

 under the action of high temperature." Certainly the experi- 

 ments of the distinguished author concerning artificial produc- 

 tion of meteoroidal substances have thrown considerable light 

 on their mode of formation ; it must, however, be stated that 

 the more crystallized these bodies are, the more remote they 

 stand in the scale of evolution from the primordial pulverulent 

 condition of their substance. It cannot be doubted that the 

 varieties of meteorites, between dust and highly crystalline iron 

 and stone-like substances, indicate distinct terms of evolution, 

 the pulverulent agglomerates in the intensely cold cosmical space 

 being heated by progressing solidification and pressure to the 

 end of their existence as cosmical bodies. The simultaneous 

 presence of heterogeneous particles within a body of notable 

 dimensions may well be supposed*. 



The lines, in the interior of meteorites, identical in com- 

 position with the enamelled crust, although of inferior forma- 

 tion, deserve some attention. Their formation probably coin- 

 cides with the consecutive and far advanced process of soli- 

 dification. As in telluric rocks, progressive evolution and mo- 

 bility of particles, even of solid substances, certainly takes 

 place in the interior of meteoric bodies, although not assisted 

 by the dissolving power of water. In places where pres- 

 sure and temperature come to their maximum, partial fusion 

 * See Vienna Acad. Proc. vol. xliii. (1861) pp. 489-526. 



Phil. Mag. S. 4. Vol. 37. No. 249. April 1869. S 



