$2o THE POPULAR SCIENCE MONTHLY, 



same general relation of light and heavy zones still exists, and that 

 the deeper we descend the more abundant the proportion of the denser 

 metals. The germ of this arrangement was undoubtedly induced in 

 the nebulous age. The compression of the surface-elements into a 

 quarter or half their known bulk cannot explain the great weight o f 

 the interior, for experiments indicate that a limit to the capacity of 

 reduction of volume is soon reached. So far as we know, the reduc- 

 tion of bulk by pressure becomes less and less in proportion to the 

 pressure exerted. 



Fig. 4. 



•Annuxar Nbbula in Lyra. 



Some interesting observations have recently been made by Prof. 

 Daubree, of Paris, upon the analogy between certain terrestrial rocks 

 and the heavy meteoric stones which occasionally fall from the sky. 

 Some of the meteorites are nearly pure iron ; others either contain 

 grains of minerals like olivine, or consist chiefly of the olivine, with 

 only occasional particles of iron. This latter class are silicates of mag- 

 nesia and the protoxide of iron, allied to the minerals olivine or peri- 

 dote, and a granular compound of anorthite and pyroxene. Patrin, so 

 long ago as 1809, called the attention of observers to the identity be- 

 tween the composition of certain meteors and substances ejected from 

 volcanoes ; and, in 1858, Yon Reichenbach sketched theoretically 

 some of the conclusions just arrived at experimentally by Daubree. 

 Reichenbach showed that most of the mineral species found in meteors 

 existed also in the trap called dolerite ; hence he inferred that masses 

 of material allied to the stony meteors are located deep down under 

 the volcanoes whence the lava was derived. Daubree has manufact- 

 ured in the furnace masses apparently identical, both with the metal- 

 lic and stony meteors. The latter were most successfully imitated by 

 melting down the mineral compounds peridote, Cherzolite, hypersthene, 

 basalt, and melaphyre. Allied to them is the dumite of New Zealand, 

 an aggregate of olivine and chromite. 





