After the death of Fraunhofer, very little was done to forward the study of spectrum analysis. Investigations in this branch of research were made, however, by Sir _John Herschel_ (1792-1871), _William Allen Miller_ (1817-1870), Sir _David Brewster_ (1781-1868), and others. Two famous men of science had partly discovered the secret. These were Sir _George Stokes_ (1819-1903), of Cambridge, and _Anders John Angström_ (1812-1872) of Upsala. Of Angström’s work, published in 1853, it has been said that it would “have obtained a high celebrity if it had appeared in French, English, or German, instead of Swedish.” It was not until 1859 that the principles of spectrum analysis were fully enunciated by _Gustav Robert Kirchhoff_ (1824-1887), and his colleague in the University of Heidelberg, _Robert Wilhelm Bunsen_ (1811-1899). Kirchhoff demonstrated that a luminous solid or liquid gives a continuous spectrum, and a gaseous substance a spectrum of bright lines. In the words of Miss Clerke, “Substances of every kind are opaque to the precise rays which they emit at the same temperature. That is to say, they stop the kinds of light or heat which they are then actually in a condition to radiate.... This principle is fundamental to solar chemistry. It gives the key to the hieroglyphics of the Fraunhofer lines. The identical characters which are written bright in terrestrial spectra are written dark in the unrolled sheaf of sun-rays.” Kirchhoff made several determinations of the substances in the Sun, proving the existence of sodium, iron, calcium, magnesium, nickel, barium, copper, and zinc. His great map of the solar spectrum was published by the Berlin Academy in 1860, and represented an enormous amount of labour. It was succeeded by another map by Angström, published in 1868. But both of these maps have been recently superseded by the investigations of Sir _Joseph Norman Lockyer_ (born 1836), and of the American physicist, _Henry Augustus Rowland_ (1848-1901). Rowland largely increased our knowledge of the elements in the solar atmosphere. The spectroscope had become, by 1868, a recognised instrument of astronomical research, and in that year it was applied during the famous total eclipse, visible in India. There were many eclipse problems, arising from the observations made by the eclipse expeditions of 1842, 1851, and 1860. The eclipse of 1851 had finally proved that the red flames seen surrounding the Sun during total eclipses belonged to the Sun, and not to the Moon, as many astronomers had believed. At the eclipse of 1860, visible in Spain, the Italian astronomer, _Angelo Secchi_ (1818-1878), and the Englishman, _Warren De la Rue_ (1815-1889), secured photographs of the solar prominences. The problem of 1868 was the constitution of these prominences.