384 Dr. J. H. Gladstone on some Points connected 



is condensable at 100° C. Again, the density of a mixture of 

 two volumes of hydrogen and one of oxygen is 6 ; but when 

 these gases are combined together, the density becomes 9. 

 Thus, again, carbon is itself very difficult to volatilize ; but its 

 compounds with oxygen, or hydrogen, or sulphur, or chlorine, 

 or nitrogen, are gaseous at the ordinary temperature or a little 

 above it. Now it is certain that in the great nebulous mass 

 the force of chemical affinity must be at work in a variety of 

 ways ; and the distance of an element from the centre of gra- 

 vity or heat will depend in no small degree upon the substance 

 with which it is combined ; nor does the chemistry of the 

 minerals which constitute the surface of our globe alibrd much 

 clue to the chemistry of an incandescent nebulous mass. We 

 may learn more from the meteorites, as they were evidently 

 formed at a very high temperature ; for they usually consist of 

 rounded masses of siliceous minerals imbedded in a matrix of 

 iron, which has all the appearance of having been soft at the 

 time of their envelopment. Now, although no element has 

 yet been found in the meteorites which does not exist in the 

 earth*, the arrangement of the elements is exceedingly differ- 

 ent. Thus we find sulphur and iron combined in the form of a 

 protosulphide (FeS), and other minerals having constitutions 

 which are unknown among those of our globe. We are not 

 free, therefore, to conclude, as Mr. Stoney is disposed to do, 

 that the vapour of barium must have a density little, if at all, 

 heavier than that of iron, since there may be light or volatile 

 compounds of barium with which at present w^e are not 

 familiar. 



V. The heads of comets have been found to be self-luminous, 

 and to emit bands which are usually referred to carbon. The 

 theory has indeed been maintained by some of our most emi- 

 nent physicists, that the minute bodies of which we have reason 

 to believe comets are composed, consist in a great measure of 

 carbon, and that in rapidly revolving round the head these 

 particles come into collision, with the production of sufficient 

 heat to volatilize the carbon. In fact, the theory maintains 

 that it is not the twinkling stars which shine like diamonds in 

 the sky, but that it is ih^ heads of comets, which are composed 



* The meteorites would appear to be a likely field for tlie discovery of 

 new elements. They will probably exist in small quantities, but recog- 

 nizable by the spectroscope ; indeed it would seem by no means impro- 

 bable that a diligent search among the residues of meteoric stones after the 

 removal of iron, silicon, magnesium, kc. Avould reveal substances which 

 would emit rays answering to some of the dark lines of the solar or stellar 

 spectra at present unrecognized. I commend this to the contideration of 

 an}^ young spectroscopist. 



