THE ORIGIN AND STRUCTURE OF METEORITES. 381 



stones as they pass through the air are followed by a tail which, at first 

 bright, soon blends itself with the darkness, like the smoke of a piece 

 of fire-works. It keeps the direction of the path of the meteor for a 

 longer or shorter time, and is undoubtedly composed of particles which 

 have become detached from the body, and remain suspended in the 

 atmosphere till they are scattered by the winds. The mode of the 

 action by which this dust is rubbed or blown off is explained by the 

 experiments I have made with explosive gases in the investigation of 

 the origin of the blister-holes of meteorites. Masses of gas at enor- 

 mous pressures almost instantaneously pulverize whatever bodies they 

 strike, and this is precisely what happens to the meteoric stones as they 

 pass through the air. Judging from the thickness of the clouds fol- 

 lowing the bodies and the space they occupy, we conclude that they 

 furnish considerable quantities of metallic and rock-dusts to our atmos- 

 phere. 



A careful investigation of the dusts which may be supposed to be 

 of cosmic origin is very desirable, as also is a systematic examination 

 of the atmosphere by all the means in our possession, after every 

 explosion of a meteor, for that which they may have left. Something 

 has been done in this direction by Mr. Phipson, M. Nordenskiold, and 

 M. Gaston Tissandier. Doubtless the shooting-stars, extreme as their 

 tenuity may be, also bring down ponderable substances in minutely 

 divided condition. The spectroscopic examination of these asteroids 

 by Mr. Alexander Herschel has revealed the presence in them of 

 sodium, magnesium, carbon, and other bodies. The fact is confirmed 

 by the formation, in connection with the extraordinary meteoric shower 

 of the 27th of November last, of a cloud of vapors which obscured all 

 the stars except those of the first three magnitudes, and was shortly 

 afterward dissipated. 



The question, whether gaseous and invisible substances may not 

 also be introduced to the earth from the realms of space, can not yet 

 be answered from observation. 



The most interesting resemblances, and even identities, are occa- 

 sionally revealed between the meteorites and some of the deeper rocks 

 of our planet. 



Volcanoes bring up daily, besides prodigious quantities of vapor 

 of water and gaseous products, melted, intensely hot stony matters, 

 which spread upon their flanks and are known as lavas. During the 

 ancient periods, there came out also, from the depths below the gran- 

 ite, rocks of a nature very different from that of the stratified rocks, 

 and presenting an analogy with the lavas. They occur on the surface 

 in various forms of sheets, cones, and irregular masses. Below it, they 

 constitute, in the thickness of the incasing rocks, a kind of columns, 

 which are connected with the extremely deep reservoirs from which 

 they have been thrown up ; they have in fact been thrust here and 

 there in consequence of eruptions, through the superposed masses, far 



