The Romance of Modern Chemistry

CHEMISTRY OF THE STARS All this is more or less by way of introduction, and we come now to the celestial problem. If a telescope is directed towards a star, a nebula, or a comet, and the light proceeding from this heavenly body is examined spectroscopically, we find, in a certain number of cases at least, a spectrum consisting of definite lines or bands, and on comparing these with the spectra already mapped, we can with confidence affirm that such and such elements are present in the far-off heavenly body. A bold step this, right out to the confines of space, and yet one which is fully warranted by the scientific evidence. In the spectrum of a nebula there are bright lines which are identical with the characteristic hydrogen lines, so that the latter element must be one of the constituents of a nebula. The spectrum of a comet is closely similar to that of the element carbon, as obtained by examination of the blue base of a candle flame; cometary matter, therefore, contains carbon. Curiously enough, as a comet approaches the sun, its spectrum alters in character, and evidence is obtained that sodium and iron also enter into its composition. Surprise is in store for us when we come to examine spectroscopically the light which comes from the sun and the great majority of the stars. Instead of getting isolated coloured lines or bands on a dark background, we observe a complete reversal of this, namely, dark lines on a coloured background (see Fig. 11). The explanation of this puzzling phenomenon is best understood perhaps by reference to an actual experiment. If we were to direct a spectroscope towards an electric arc light, in which there is incandescent solid carbon, we should observe a continuous spectrum. Suppose now that between the spectroscope and the arc light 210