32 COSMOS. 



The whole may in accordance with the present state of our 

 knowledge be arranged in the following manner : 



Sliehallien, according to the mean of the maximum 

 4.867 and the minimum 4.559, as found by Play- 

 fair 4.713 



Mont Cenis, observations of Carlini, with the cor- 

 rection of Giulio, 4.950 



The torsion-balance, Cavendish (according to Baily's 



calculation) . 5.448 



Reich, 1838 5.440 



Badly, 1842 5.660 



Reich, 18471850 5.577 



The mean of the two last results gives 5. 62 for the density 

 of the earth (taking that of water as 1), and consequently 

 much more than the densest finely granular basalt, which 

 according to the numerous experiments of Leonhard varies 

 from 2.95 to 3.67, and more than that of magnetic iron (4,9 

 -to 5.2), and not much less than that of the native arsenic of 

 Marienberg or Joachimsthal. We have already elsewhere 

 observed (Cosmos, vol, i, p. 159) that from the great distribu- 

 tion of secondary and tertiary formations, and of those up- 

 heaved strata which constitute the visible continental part of 

 our earth's surface (the plutonic and volcanic upheavals 

 being scattered in the form of islands over a small area of 

 space), the solid portion of the upper part of the earth's crust 

 possesses a density scarcely reaching from 2.4 to 2.6. If we 

 assume with Rigaud that the relation of the solid to the 

 fluid oceanic surface of our globe is as 10 : 27, and if further 

 we consider that the latter has been found by experiments 

 with the sounding lead to extend to a depth of 27,700 feet, 

 the whole density of the upper strata, which underlie the dry 

 and oceanic surfaces, scarcely equals 1.5. The distinguished 

 geometrician Plana has correctly observed that the author of 

 the jftlecanique Celeste was in error, when he ascribed to the 

 upper stratum of the earth a density equal to that of granite, 



balance, a method that had been first suggested by Reich, and was 

 employed by Gauss in his magnetic observations. The use of such a 

 mirror, which is of great importance from the exactness with which 

 the scale may be read off, was proposed by Poggendorfi' as early as the 

 year 1826 (Annakn der Physik. Bd. vii, s. 121) 



