CHEMISTRY OF THE EARTH. 185 



This nebulous matter is conceived to be so intensely heated as to be in 

 the state of true gas or vapor, and, for this reason, feebly luminous 

 v\"hen compared with the sun. It ^vould here be out of place to discuss 

 the detailed results of spectroscopic investigation, or the beautiful and 

 ingenious methods by wliich modern science has shown the existence in 

 the sun, and in many other luminous bodies in space, of the same chem- 

 ical elements that are met with in our earth. 



§ G. Calculations based on the amount of light and heat radiated from 

 the sun show that the temperature which reigns at its surfiice is so great 

 that Ave can hardly form an adequate idea of it. Of the chemical rela- 

 tions of such intensely heated matter modern chemistry has made known 

 to us some curious facts, which help to throw light on the constitution 

 and luminosity of the sun. lleat, under ordinary conditions, is favor- 

 able to chemical combination, but a higher temperature reverses all 

 affinities. Thus, the so-called noble metals, gold, silver, mercury, &c., 

 unite with oxygen and other elements ; but these compounds are decom- 

 posed by heat, and the pure metals are regenerated. A similar reaction 

 was many years since shown by Mr. Grove with regard to water, whose 

 elements — oxygen and hydrogen — when mingled and kindled by flamCj 

 or by the electric spark, unite to form water, which, however, at a much 

 higher temperature, is again resolved into its component gases. Hence, 

 if we had these two gases existing in admixture at a very high tempera- 

 ture, cold would actually effect their combination precisely- as heat would 

 do if the mixed gases were at the ordinary temperature, and literally it 

 would be found that " frost performs the effect of fire."' The recent re- 

 searches of Henry Sainte-Claire Deville and others go far to show that this 

 breaking-up of compounds, or dissociation of elements by intense heat 

 is a principle of universal application ; so that we may suppose that all 

 the elements which make up the sun or our planet would, when so in- 

 tensely heated as to be in .that gaseous condition which all matter is 

 capable of assuming, remain uncombined, that is to say, would exist 

 together in the condition of Avhat we call chemical elements, whose fur- 

 ther dissociation in stellar or nebulous masses may even give us e\i- 

 dence of matter still more elemental than that revealed by the experi- 

 ments of the laboratory, where we can only conjecture the comiiound 

 nature of many of the so-called elementary substances. 



§ 7. The sun, then, is to be conceived of as an immense mass of intensely 

 heated gaseous and dissociated matter, so condensed, however, that not- 

 withstanding itsexcessive temperature, it has a specific gravity not much 

 below that of water ; probably offering a condition analogous to that 

 which Cagniard de la Tour observed for volatile bodies when submitted 

 to great pressure at temperatures much above their boiling point. The 

 radiation of heat going on from the surface of such an intensely heated 

 mass of uncombined gases will produce a superficial cooling, which will 

 permit the combination of certain elements, and the production of solid 

 or liquid particles ; these, suspended in the still dissociated vapors, 

 become intensely luminous, and form the solar photosphere. The con- 

 densed particles, carried down into the intensely heated mass, again 

 meet with a heat of dissociation, so that the process of combination at 

 the surface is incessantly renewed, while the heat of the sun may bo 

 supposed to be maintained by the slow condensation of its mass ; a dim 

 inution by jiufot^ ^^ i^'^ present diameter being sufficient, according to 

 Helmholtz, to maintain the x^resent supply of heat for twenty-one thou- 

 sand years. 



§ 8. This hypothesis of the nature of the sun and of the luminous 

 process going on at its surface is the one lately put forward by Faye, 



