POTASSIUM, RUBIDIUM, CAESIUM, AND LITHIUM 561 



and gaseous matter, 33 including those elements whose reversed spectra 

 correspond with the Frauenhofer lines namely, sodium, iron, hydrogen, 

 lithium, calcium, magnesium, tkc. Thus in spectrum analysis we find 

 a means of determining the composition of the inaccessible heavenly 

 luminaries, and much has been done in this respect since Kirchhoff's 

 theory was formulated. By observations on the spectra of many 

 heavenly bodies, changes have been discovered going on in them, 34 and 

 certain of the elements known to us have been found with certainty in 

 them. 3 "' From this it must be concluded that the same elements which 

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



35 Eruptions, like our volcanic eruptions, but on an incomparably larger scale, are a 

 frequent occurrence on the sun. They are seen as protuberances visible during a total 

 eclipse of the sun, in the form of vaporous masses on the edge of the solar disc and 

 emitting a faint light. These protuberances of the sun are now observed at all times by 

 means of the spectroscope (Lockyer's method), because they contain luminous vapours 

 (giving bright lines) of hydrogen and other elements. 



54 The great interest and vastness of astro-physical observations concerning the sun, 

 comets, stars, nebulae, &c., render this new province of natural science very important, 

 and necessitate referring the reader to special works on the subject. I cannot, how- 

 ever, but caution the reader against those premature conclusions which many form on a 

 first acquaintance with the subject. Just as the astromomer may easily arrive at an 

 arbitrary conclusion about the composition of elements, from observations upon the 

 spectra of the heavenly bodies, so the chemist may easily fall into error as to the nature 

 of the phenomena of the heavens by only judging from spectroscopic observations. 



The most important astro-physical data since the time of Kellner are those referring 

 to the displacement of the lines of the spectrum. Just as a musical note changes its 

 pitch with the approach or withdrawal of the resonant object or the ear, so the pitch of 

 the luminous note or wave length of the light varies if the luminous vapour and the 

 earth from which we observe it approach or recede from each other ; this expresses 

 itself in a visible displacement of the spectral lines. The solar erruptions 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 its mass, which must be pronounced as 

 vaporous, and in its atmosphere, are now studied by means of the spectroscope. For 

 this purpose, there now exist many special astro-physical observatories where these 

 investigations are carried on. 



35 Spectrum analysis has proved the indubitable existence in the sun and stars of 

 a number of elements known in chemistry. Huggins, Secchi, and others have furnished 

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

 on this subject has been given by Prof. S. A. Kleiber, in the Journal of the Kussian 

 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 nearD), which is seen very brightly in the projections (protuberances) 

 and spots of the sun, but which does not belong to any known element and is not repro- 

 ducible as a reversed, dark line. This may be a right conclusion that is to say, it is pos- 

 sible 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 428, at the very end 



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