those who listened to him at Cardiff may perhaps remember, he described the memorable discoveries by which he extended the methods of spectrum analysis to several of the heavenly bodies. He showed the spectra which he and the late Professor Miller had already succeeded in obtaining of some of the brightest stars, notably of Aldebaran and Betelguese. He had measured the dark lines with which the spectra of these stars were crowded, and it was shown by their positions that certain well-known terrestrial substances must be present in those distant luminaries. In reference to many of these elements the coincidence is based not on one line but on several lines, so that it is impossible to shake the testimony which the spectroscope affords as to the identity, in part at all events, of the constituents of the stars with the materials in the solar system.
On referring to this memorable lecture of 1866, it is indeed surprising to find how discoveries seemed to crowd together at the commencement of Sir William Huggins' career. He had at that time noticed the characteristic spectrum presented by white stars, of which Sirius is one type, and had demonstrated the existence of hydrogen in stars of this class. He had also examined coloured stars, like Alpha Herculis, and had found them to exhibit a spectrum, in which portions of the coloured bands are subdued by strong groups of lines in such a way as to afford an explanation of the hues which these stars display. He had demonstrated in the case of Beta Cygni that sufficient lines are found in the blue and violet parts of the spectrum of the large star to make the red and yellow rays predominate, thus giving to the lustre of the larger star of this celebrated pair a hue that is often known as
