THE aREAT IOWA METEOR. 595 



A trace of mauganese remains with the ferrous oxide also a small 

 amount of alumina. The trace of sodium is sufficient to give a brilliant 

 line in the spectroscope ; the lithium-line, while quite distinct, is not 

 bi'illiant. 



An extended report of my examination of the Iowa County meteor- 

 ite will be published, as soon as the more careful investigation of the 

 concretions shall have been completed, which examination is delayed 

 for want of material. I am unwilling to sacrifice any of the fine speci- 

 mens above enumerated for this purpose. 



III. The Oeigij^ of Meteoeites. The researches of Daubree and 

 Meunier, of Paris, have demonstrated that meteorites are fragments 

 of one or more planetary bodies, which, by some great convulsion, has 

 been broken to pieces. Furthermore, we possess abundant evidence 

 that the earth, in its structure, corresponds, at different depths, to the 

 different varieties of meteorites : from those without iron (Asyderes), 

 through the Oligosideres to those consisting exclusively of nickelifer- 

 ous iron (Syssyderes). Hence if our earth, through the action of some 

 cause, should be broken to pieces, these pieces would be meteorites and 

 describe orbits around the sun similar to and near by the orbit of the 

 earth. 



But the cosmical spaces are filled with a very rare, slightly-resist- 

 ant medium. Hence, the fragments being different in density and in 

 dimensions, would be differently affected by this resisting medium. 

 The smaller fragments and those of less density would lose their ve- 

 locity of revolution around the sun more rapidly than those of greater 

 size and higher density. In other words, all fragments would, while 

 revolving around the sun, also descend toward the same, bat at differ- 

 ent rates : the smaller and lighter fragments would sink faster than 

 the larger and heavier. 



These terrestrial meteorites would, therefore, gradually reach the 

 orbits of the inner planets. On Venus first would appear meteorites 

 composed of the rocks of our earth's superficial crust, limestone, shales, 

 quartz, granite, serpentine, etc. These would be associated with small 

 meteorites of more dense materials derived from the deeper portions of 

 the earth. At a later period, Venus would receive terrestrial meteorites 

 from deeper portions of our earth, corresponding to Oligosideres. 

 These would also be associated with small meteorites of denser mate- 

 rials, thus foreshadowing the third meteorite era, in which the dense 

 masses of the interior metallic core of our earth would have sunk far 

 enough toward the sun to reach the orbit of Venus. The mechanical 

 problem herein involved I pretty completely solved about ten years 

 ago.' 



Now, it is furthermore well understood that it will be a long time 



' "On the Density, Rotation, and Relative Age of the Planets," American Journal 

 of Scie>ics, 1864, vol. xsxvii. " Introduction to the Mathematical Principles of the Nebu- 

 lar Theory, or Planetology," America7i Journal of Sciences, 1865, vol. xxxix. 



