LAND AND WATER 35 



continuous rise of temperature cannot change to a fall which 

 eventually reaches freezing point. Assuming that the 

 geothermic degree remains constant and equal at 100 degrees, 

 a figure not far from the observed mean, the temperature of 

 the earth's centre situated at a depth of 6,350,000 metres would 

 be found to be 63,500 degrees — which is quite a different 

 matter, but manifestly impossible, for this would be higher than 

 the temperature attributed to the surface of the sun. 



These contradictory data suffice to show how little we should 

 know of the interior constitution of the earth if it were not for 

 other facts which have recently come to l.'ght. The study of the 

 lava from volcanic eruptions has led to the assumption that 

 below the solid crust or lithosphere there exists a continuous 

 molten mass, the Pyrosphere, constituted by a magma 

 containing iron and magnesium. This becomes increasingly 

 homogeneous as the depth increases, tending to approach, in 

 composition, that of silicate of iron and magnesium, which 

 mineralogists call peridot. 1 Peridot, deeply situated, is always 

 associated with iron. This association is exactly reproduced 

 in the meteorites studied by Daubree and M. Stanislas Meunier, 

 and has led them to consider these as the scattered debris of 

 a star, or possibly a residual planet, approximately con- 

 temporaneous in origin with the earth, formed at the expense 

 of the sun, and with an orbit crossing ours periodically. 2 The 

 composition of these meteorites may therefore be compared to 

 that of the earth's core called the barysphere. This barysphere, 

 in the main, would be formed by a metallic iron associated with 

 nickel, a sort of steel. In this way the resemblance of its 

 properties to those of a magnet and its power of directing a 

 compass would be explained. Nickel-steel would thus be the 

 essential metal and constitute the universal basis of the earth's 

 crust. 



The study of earthquakes has corroborated this conclusion 

 in a manner as unexpected as it is exact. After numerous 

 more or less clumsy attempts, an automatic registering 

 apparatus has been constructed of such a degree of sensibility 



1 The chemical formula of peridot is (MgO.FeO) 2 Si0 2 . 



2 It is difficult to assume that this star was a former satellite of the earth 

 like the moon. The debris of such a satellite would have formed a ring round 

 the earth or would have revolved round it like the moon, before falling 

 to its surface as soon as its tangential acceleration had sufficiently slackened. 

 This does not seem to be the case with meteorites which occur in " swarms " 

 whose orbit rather resembles that of comets. 



