570 PEINCIPLES OF CHEMISTRY 



many of the elements known to iis have been found with certainty in 

 them. 35 from this it must be concluded that thte same elements which 

 exist on the earth occur throughout the whole universe, and that at 

 that degree of heat which is proper to the sun those simple substances 

 which we accept as the elements in chemistry are still undecomposed 

 and remain unchanged. A high temperature forms one of those 

 conditions under which compounds most easily decompose ; and 

 if sodium or a similar element were a compound, in all probability 

 it would be decomposed into component parts at the high temper- 

 ature of the sun. This may indeed be concluded from the fact that 

 in ordinary speetroscopic experiments the spectra obtained often 

 belong to the metals and not to the compounds taken ; this depends 

 on the decomposition of these compounds in the heat of the flame. If 



expresses itself in a visible displacement of the spectral lines. The solar eruptions even 

 give broken lines in the. spectrum, because the rapidly moving eruptive masses of vapour 

 and gases either travel in the direction of the eye' or fall back towards the sun. As the 

 earth travels with the solar system among the stars, so it is possible to determine the 

 direction and velocity with which the sun travels in space by the displacement of the 

 spectral lines and light of the stars. The changes proceeding on the sun in ks mass, 

 which must be pronounced as vaporous, and in its atmosphere, are now studied by 

 means of the spectroscope. For this purpose, many special astro- physical observatories 

 now exist where these investigations are carried on. 



We may remark that if the observer or luminous object moves with a velocity 



v, the ray, whose wave-length is A, has an apparent wave-length A . v , where n is the 



n 



velocity of light. Thus Tolon, Huyghens, and others proved that the star Aldebaran 

 approaches the solar system with a velocity of 80 kilometres per second, while Arcturus 

 is receding with a velocity of 45 kilometres. The majority of stars give a distinct 

 hydrogen spectrum, besides which nebulae also give the spectrum of nitrogen. Lockyer 

 classes the stars from their spectra, according to their period of formation, showing that 

 some stars are in a period of increasing temperature (of formation or aggregation), 

 whilst others are in a period of cooling. Altogether, in the astro-physical investigation 

 of the spectra of heavenly bodies we find one of the most interesting subjects of recent 

 science. 



55 Spectrum analysis has proved the indubitable, existence in the sun and stars of a 

 number of elements known in chemistry. Huyghens, Secchi, Lockyer, and others have 

 furnished a large amount of material upon this subject. A compilation of existing 

 information on it has been given by Prof. S. A. Kleibet, in the Journal of the 

 Russian Physico-chemical Society for 1885 (vol. xviii. p. 146). Besides which, a peculiar 

 element called helium has been discovered, which is characterised by a line (whose wave- 

 length is 587'5, situated near D), which is seen very brightly in the projections (pro- 

 tuberances) and spots of the sun, but which does not belong to any known element, and 

 is not reproducible as a reversed, dark line. This may be a right ^conclusion that is to 

 say, it is possible that an element may be discovered to which the spectrum of helium 

 corresponds but it may be that the helium line belongs to one of the known elements, 

 because spectra vary in the brilliancy and position of their lines with changes of 

 temperature and pressure. Thus, for instance, Lockyer could only see the line 423, at 

 the very end of the calcium spectrum, at comparatively low temperatures, whilst the 

 lines 897 and 898 appear at a higher temperature, and at a still higher temperature the 

 line 423 becomes quite invisible. 



