It remained for Bunsen and Kirchhoff, in 1860, to point out the fact that these dark lines were characteristic of certain chemical elements existing in the sun and its photosphere, and this fact is the foundation of spectrum analysis. The broad black band in the sun’s spectrum, called by Fraunhofer D, corresponded exactly in position and in width with the yellow band produced by a flame containing incandescent sodium. There was no doubt whatever, therefore, that the two phenomena were due to the same cause; but why in the one case should the band be black and in the other yellow? This question was answered by the discovery of the fact that a ray of light colored by incandescent sodium, passing through a luminous atmosphere of the same metal, would lose by absorption all of its yellow color, and would display a black band where before the yellow color existed. Based upon this observation, the development of spectrum analysis went forward with amazing rapidity. The hundreds of lines in the sun’s spectrum were found to occupy exactly the position of luminous lines in the spectra of various metals, and thus it was possible for the chemist to extend his investigations beyond the limits of the earth, and distinguish the chemical elements in the sun and in the fixed stars billions of miles farther away from us than the sun itself. Celestial chemistry has thus become a fixed and definite science. But the value of spectral examinations has extended still farther. Many luminous lines were observed in the spectrum which were not found in the spectra of any known element. The inference then logically arose that there were elements yet undiscovered to which these lines were due. From this starting point investigations proceeded which have led to the discovery of a large number of elementary bodies. Among the important elements that have been discovered by means of spectrum analysis may be mentioned: cæsium, rubidium, thallium, indium, gallium, ytterbium, and scandium. Spectrum analysis is also extremely useful in proving the verity of supposed new elements; for if a supposed new element should be found to give a series of spectral lines coincident with those already known, it would be a positive proof of the fact that the supposed new element was but a mixture of bodies already known to exist. V. SYNTHETICAL CHEMISTRY.