826 POPULAR SCIENCE MONTHLY. 



volcanic ejections. After the mighty eruption of Krakatoa, for 

 example, I sought in vain for these elements in the cinders cast out, 

 which probably came from great depths. The supposed discovery 

 of a new element in the ancient lavas of Vesuvius has been found 

 to be erroneous. 



Elementary bodies seem to multiply as we approach the surface 

 of the globe. Two hypotheses suggest themselves in explanation 

 of the fact: that of displacements of cosmical matter, and that of 

 the new formation of elements on the surface. 



The displacements of cosmic materials are incessant; falls of 

 meteorites furnish a particularly striking example of them, but it 

 is probable that as to quantity the cosmical dusts are of more impor- 

 tance. Yet neither the meteorites found at various points nor the 

 dust collected by Nordenskiold in the ice fields of the polar regions, 

 the extra-terrestrial origin of which can not be doubted, contain 

 the rare elements of the earth. The hypothesis of an increase by 

 accretions from without appears to lack foundation. 



The new formation of elementary bodies seems to be still less 

 probable; at most it might be explained by the possibility, often 

 indicated but never established, of a new reduction of bodies here- 

 tofore supposed to be simple. Spectrum analysis, it is true, reveals 

 to us transformations which are gradually going on in the matter of 

 the fixed stars, but they are only of known substances becoming con- 

 verted into other substances equally known. Moreover, the con- 

 ditions of temperature and aggregation of the fixed stars and those 

 of the earth can not be compared. 



It is evident that the increase of simple bodies in the outer strata 

 of the earth is only apparent. It should be recognized, besides, that 

 science has made great progress, and this progress can not be with- 

 out influence on the discovery of new substances. The first electro- 

 lytic decompositions accomplished by Davy with an inferior vol- 

 taic pile made known at the beginning of this century the existence 

 of metallic radicles in the salts and the earth of which there had not 

 been before the slightest suspicion; while Moissan, by the employ- 

 ment of the powerful currents now available, has been able to 

 disengage fluorine — hitherto almost unknown — from its combina- 

 tions. Spectrum analysis has cast light on a whole series of ele- 

 ments of characteristic spectra. The presence of one of these ele- 

 ments, helium, had been demonstrated in the sun before it was 

 known that it likewise entered into the composition of our globe. 

 The conclusions drawn by D. Mendeleef from the periodical law 

 have also led to the discovery of several elements the existence of 

 which was indicated by theory before the chemist had isolated them. 

 I mention, first, scandium, discovered in 1879 by Nilson in exonite, 



