242 



ELEMENTS, COMPOSITE NATURE OF TIIE. 



existence of all the elements found on the earth, 

 even if it were positively known that only the 

 lighter gases were present in the parent nebu- 

 lae." This theory accounts for the presence in 

 the nebulio of a substance not present in the 

 solar system, which is assume! to have once 

 passed through tin- same physical condition, 

 associated with other substances which are in- 

 dubitably abundant in the sun and its planets, 

 and for many substances present in the earth, 

 some of which have been detected in the sun 

 and stars, and numerous others of which are 

 probably contained in them, of which no traces 

 are found in the nebular spectra. It also ex- 

 plains how these substances could have been 

 derived from the nebular mass when their ex- 

 istence in a volatile state would necessitate a 

 temperature far higher than can bo supposed 

 to have ever prevailed throughout the original 

 nebula. Those elements which have the high- 

 est melting and volatilizing points are precisely 

 those which have the greatest atomic weight, 

 and aro therefore the most likely to be of 

 composite nature; while those which have 

 the lowest combining numbers, and are there- 

 fore more likely to be simple substances, are 

 those which have as a rule extremely low con- 

 densing points. Carbon, which, with an atom- 

 ic weight of 12, assumes solid forms at ordi- 

 nary temperatures, and mercury, which can be 

 vaporized at a low temperature, while its com- 

 bining number is in the new system 200, are 

 the only exceptions to this rule. A law in ex- 

 perimental chemistry is, that the increase of 

 mass in the formation of compound molecules 

 is attended with a decrease of stability. Many 

 ^f the metallic and metalloidal elements com- 

 oine in larger molecular masses than are pos- 

 sessed by many compound substances. If they 

 are the products of the metamorphosis of lost 

 elementary substances at a time when the heat 

 of the nascent solar system was greatest, they 

 can not be expected to be resolved into their pri- 

 mary constituents by human means. Those of 

 them which are found in the sun may be sus- 

 pected to belong to this category. Those which 

 are found only in the earth may be compounds 

 formed at a lower temperature. Many mole- 

 cules of hydrogen, or of nitrogen, carbon, or 

 oxygen, might be contained in a molecule of 

 gold, of platinum, or of lead. 



It is consonant with the atomic theory to 

 consider the stability of the elements as only 

 relative. Even the molecule of hydrogen, 

 which is taken as the standard and nnit of 

 molecular measurement, may be u superior form 

 of atomic arrangement. There may be sub- 

 stances with minuter and simpler molecules 

 which can not be appreciated by the senses, 

 and do not respond to the physical law of at- 

 traction to a measurable extent. The impon- 

 derable interstellar ether is matter which is 

 not visibly subject to the influence of gravita- 

 tion. Possibly there exist atomic aggregates 

 of still lower order. All known substances 

 may have been evolved from antecedent forms 



of matter. The process of evolution is seen to 

 go on in all the known forms of matter, and 

 the evolution of matter with an altered molec- 

 ular constitution would naturally be supposed 

 to have attended the other physical changes in 

 the history of nebula? and their consolidation 

 into planetary systems. The anomalous phe- 

 nomena of ozone and antozone bring into ques- 

 tion the absolute stability of the presumably 

 simplest and most elementary substances. The 

 unknown substance which gives out the green 

 ray in the solar spectrum has been conjectured 

 to be of simpler constitution than any of the 

 terrestrial elements. 



In the various homologous series of hydro- 

 carbons the boiling-point of the compounds 

 rises, and their specific gravity increases, with 

 their molecular complexity or increase in molec- 

 ular weight. The broadest and most securely 

 established general law in chemistry is that 

 substances with the lowest atomicity have the 

 lowest melting-points and the simplest spectra, 

 and that both these functions are in a general 

 way proportional to the combining number 

 of a substance. The hypothesis of variable 

 molecular groupings under different conditions 

 within the so-called elements explains many 

 facts which are now anomalous. It accounts 

 for the irregular vapor densities of some sub- 

 stances. The phenomenon of allotropism ex- 

 hibited by various metalloids, which is most 

 marked with those which have not been found 

 in the sun, is thus explained. The allotropic 

 substances exhibit complex spectra, and their 

 spectra are often different for the different al- 

 lotropic states. In passing from one allotro- 

 pic condition to another, energy is invariably 

 evolved or absorbed, which can only be ac- 

 counted for on the supposition that it controls 

 changes in the molecular disposition of the 

 atoms. The phenomena of polymerisin in or- 

 ganic substances can only be explained by the 

 theory of the variability of constitution of sub- 

 stances known to us as primary. The spec- 

 trum of potassium varies exceedingly at dif- 

 ferent temperatures, and the spectra present 

 a marked analogy to those of hydrocarbons 

 evolved during fractional distillation. 



The coincidence of some of the bright lines 

 in the spectra belonging to different metals 

 was first noticed by Kirchhoff. The bright- 

 est stars give only a few prominent lines, 

 and these are the same as those which show 

 bright in the spectrum of the solar disk. In 

 Sirius there are only half a dozen well-marked 

 lines. The cold stars, which give a feeble 

 and reddish light, have fluted spectra instead 

 of lines. The fluted spectrum of any sub- 

 stance gives place at higher temperatures to 

 the line-spectrum characteristic of the same 

 substance ; and when the elevation of temper- 

 ature is gradual, the bright lines of an element 

 appear in the same way in which the lines of 

 the constituents of a compound appear, instead 

 of the spectrum of the compound when the 

 latter is broken up. In the laborious spectrum 



