The Romance of Modern Chemistry

CHEMISTRY OF THE STARS study of the light which comes to us from the heavenly bodies, in other words, on the use of spectrum analysis. When white light, such as is obtained from the upper part of a candle flame, is passed through a slit at the end of a telescope, and then through a glass prism, it is seen as a strip which is red at one end, violet at the other, and between these two extremes passes continuously through the various shades of orange, yellow, green, and blue. This strip of graded colour is known as a con- tinuous spectrum, and it results from the splitting up of white light into its various components, which is effected by the prism. The apparatus consisting of all the necessary parts for the production and observation of a spectrum is known as a spectroscope, and this is the instrument which has yielded such marvellous results in the study of the sun and stars. If we were to examine with a spectroscope the light given out by a red-hot poker we should see only the red end of the spectrum. If the poker were put in the fire again and its temperature were raised, the spectrum observed would show some orange and yellow as well as red, while if we brought the poker to a white heat and examined it in this condition with the spectroscope, we should see a spectrum perfectly continuous from the red to the violet end. Molten iron also would exhibit a continuous spectrum, and one can say generally that the spectrum of the light emitted by any incandescent solid or liquid is continuous. It is quite easy, however, to get an incomplete spectrum, one which consists only of isolated lines or bands of different colours. In order to do that we have merely to examine with the spectroscope the light which is emitted by an incandescent vapour. One of the simplest spectra 206