ELEMENTS, COMPOSITE NATURE OF THE. 



241 



pounds formed from the union of other com- 

 pounds, is the usual manner in which the 

 minerals of the earth's crust were formed. 

 The metamorphic combinations through which 

 the chemical constituents of organic substances 

 pass are sfill more complex. Since the many 

 thousand substances which are found on the 

 earth have been resolved into a limited number 

 of bodies, it may be expected that improved ex- 

 perimental methods will discover the compound 

 character of some of them, and that perhaps 

 whole groups of the present elements will give 

 way to analytical experiments, as did the alka- 

 lies and earths which were regarded as primary 

 substances at the beginning of this century. 

 Nor, when the limited means which we possess 

 for overcoming the cohesive force of molecules 

 are considered, can it be taken for granted that 

 any of the supposed elements possess the atomic 

 constitution and physical properties of the sub- 

 stances which composed the solar universe 

 when the solid bodies of the planets and the 

 liquid mass of the sun were dissolved into one 

 fiery, gaseous flux, whose molecular particles 

 developed a heat in their collisions far beyond 

 that of the sun. 



Recent scientific speculation conjectures a 

 cold nebular condition anterior to the luminous 

 nebular period. It is supposed that, among the 

 phases through which the stellar systems pass, 

 may be one in which the gaseous matter is 

 dispersed so widely in space that the flying 

 molecules do not impinge upon each other with 

 sufficient frequency to produce the manifesta- 

 tions of heat and light. In that condition the 

 division of matter may have been finer, and its 

 constitution more homogeneous, than when it 

 was drawn together, in accordance with the 

 most universal law which science has estab- 

 lished that of the mutual attraction of bodies 

 into closer contact. The elements whose 

 existence seems to be best established in the 

 hotter stars and the nebulas are the primary 

 gases of the earth's surface hydrogen, oxygen, 

 nitrogen. Hydrogen seems to be present in all 

 luminous bodies which have been examined 

 with the spectroscope, where it occupies a po- 

 sition in the outer atmosphere. Nitrogen is the 

 only other terrestrial substance whose presence 

 in the nebulaa is ascertained. It has not been 

 detected in the solar spectrum, but this is 

 probably owing to the difficulty of determining 

 the composition of a fused mass enveloped in 

 an atmosphere of incandescent gases. As it 

 forms so large a proportion of the earth's at- 

 mosphere, it must be inferred from the nebular 

 hypothesis that it exists in the central body, 

 which constitutes nearly T Wg- of the total mass 

 of the solar system, unless it also be supposed 

 to be one of the substances which have come 

 into being during the process of cooling. Its 

 presence in the incandescent nebulae, its gaseous 

 nature, and its probable simple molecular con- 

 stitution, indicated by its light atomic weight, 

 render this an unlikely supposition. The recent 

 discovery of oxygen in the sun illustrates the 

 VOL. xxi. 16 A 



difficulty of reading the solar spectrum, and 

 strengthens the expectation of finding nitrogen 

 and perhaps numerous other unobserved bodies 

 in the suu. 



The nebular spectra seem to be simpler than 

 those of any of the solar bodies. Besides the 

 two gases mentioned, the only other substance 

 observed which projects a well-defined line is 

 an unknown element whose spectrum resem- 

 bles that of barium ; but the proximity of its 

 line to the barium line is supposed to be purely 

 accidental. This, like the two known sub- 

 stances which have been identified in the neb- 

 ulsB, may be presumed to be a gas of light 

 atomic weight, which preserves the gaseous 

 form at exceedingly low temperatures. In the 

 formation of the solar system from a diffused 

 nebulous mass, the kinetic theory would require 

 that the gaseous materials should rise in tem- 

 perature as they are brought into closer and 

 closer compass before condensing into liquid 

 forms. The hypothesis is that the unknown 

 substance which has been discovered in the 

 nebulae, or substances if there are more such, 

 was also represented in the solar system when 

 in the nebular state ; and that, when the gases 

 were compressed more and more closely around 

 the nuclear mass in obedience to the princi- 

 ple of gravitation, the rise of temperature 

 which attended the process transformed these 

 substances, while the other gases remained 

 stable. 



The theory was thus stated by Lester F. 

 "Ward in a meeting of the Philosophical So- 

 ciety of Washington : " Prior to the stage in 

 the history of a nebula at which the degree of 

 molar aggregation is sufficient to occasion a 

 great amount of friction among the particles, 

 the temperature of the primary molecular ag- 

 gregates must be nearly that of space, and it 

 can rise only as increase of density and molar 

 motion increases that friction, and converts 

 material motion into ethereal vibration. Neb 

 ulse must therefore possess a long history, of 

 which neither the telescope nor the spectro- 

 scope can furnish any record the pre-lumi- 

 nous period in which, of course, no gases can 

 exist except those, like hydrogen and nitrogen, 

 which maintain their gaseous form under ex- 

 tremely low temperature. And it may be sup- 

 posed that during this period other gases may 

 exist associated with these, which, however, 

 unlike them, are unable to sustain the succes- 

 sively higher and higher temperatures which 

 the nebula acquires in its process of conden- 

 sation and organization into a system, and at 

 certain stages of this process are dissociated 

 and resolved into aggregates of a different con- 

 stitution, suited to these temperatures. Some 

 of the latter new aggregates would naturally 

 assume the liquid and solid forms at temper- 

 atures still high as compared with those to 

 which we are accustomed, and constitute in 

 the cooled-off crust of the planets the various 

 metals and metalloids. In this manner we 

 should have no difficulty in accounting for the 



