ON THE PEOGRESS OF SCIENCE. XI 



oxides similar to those which belong to onr own planet. M. Dau- 

 bi'ee, before the French Academy, has given the chemical and 

 mineralogical chai'acters of meteorites, and finds that their sim- 

 ilariL}' to terrestrial rocks increases as we penetrate into the crust 

 of the earth, and that some of our deep-seated minerals, as olivine, 

 serpentine, etc., are almost identical with meteoric constituents. 

 When we consider that the exterior of the earth is oxidated to a 

 considerable extent, there is no cause for wonder that its deox- 

 idated interior should possess a higher specific gravity than the 



Cl'USt. 



The asteroids and planets now number ninety-two, and proba- 

 bly the next half century will demonstrate that the now seeming- 

 ly vacant interjilanetary spaces are occujiied by many others of 

 these bodies. 



Our own satellite has been the subject of rigid scrutiny, yet the 

 question whether the moon possesses any atmosphere cannot be 

 regarded as solved ; if there be any, it must be exceedingly 

 small in quantity and highly attenuated. It is believed that there 

 is not oxygen enough in the moon to oxidate the metals of which 

 it is composed, and that the surface which we see is metallic, or 

 nearly so. M. Chacornac's recent observations lead him to the 

 belief that many of the lunar craters were the result of a single 

 explosion, which raised the surface as a bubble, and deposited the 

 dihris around the orifice of ei'uption. The lunar eruptions evi- 

 dently did not take j^lace at one period only, as in many parts one 

 crater is seen encroaching on and displacing others. 



It is to be hoped that the achromatic telescope will ere long be 

 freed from its old and great defect, " the inaccuracy of definition, 

 arising from what was termed the irrationality of the spectrum, or 

 the incommensurate divisions of the spectra, formed by flint and 

 crown glass." 



The improvements of Mr. Alvan Clark, of Cambridge, Mass., 

 in the construction and local correction of lenses for the telescope, 

 for which the Rumford JNIedal has recently been awarded by the 

 American Academy, mark a new era in astronomical observation. 

 . Eecent discoveries in palseontology prove that man existed on 

 this earth at a j)eriod far anterior to that commonly assigned to 

 him. The chipped flints of the earliest races show that their con- 

 dition was not that of civilization ; to these rude implements suc- 

 ceeded more carefully shaped and polished stone weapons, then 

 bronze was used, and, the last, before the historic period, iron. 



