Page:Gods Glory in the Heavens.djvu/153

Rh flame of a burner. The light of the burner has only to be transmitted through the prism in order that it may yield the secret.

The grand discovery, in reference to solar chemistry, is the meaning of the dark lines in the solar spectrum. Besides the bands of the seven primitive colours, there are innumerable black lines which cross the spectrum, and divide the colours into very narrow stripes. In the cut, the diagram of lines must be conceived as superimposed on that of the colours. These lines are seen when the sun's rays are passed through a narrow slit before falling on the prism. If a large beam be taken instead, they cannot be detected, as, in this case, the spectrum is composed of several spectra, overlapping one another and confusing the details. These dark markings are called Frauenhofer's lines. The principal ones are designated by the letters B, C, D, E, F, G, H, and occupy preciselydefined positions in the spectrum. But besides these, there are thousands more; every new refinement in observation detects additional ones. These dark lines have long formed an enigma to physicists. It was plain, that they indicated, that some of the rays were somehow absorbed or obstructed. If we lay a comb on a piece of coloured paper, the teeth will obstruct the view of the paper under them, so that we can see the colour of the ground only in the spaces between the teeth. This is precisely what is seen in the spectrum; the whole coloured spaces