first accurate knowledge of the spectrum of hydrogen should have been ascertained not from a course of refined laboratory experiments, but from photographs of the spectra of the white stars to which Sirius belongs. Hydrogen has a few visible lines in its spectrum, and the photograph shows that these belong to an organized system of lines which are wonderfully displayed in the spectra of the white stars, first fully obtained by Sir W. Huggins. The hydrogen spectrum possesses a special interest, inasmuch as Dr. Johnstone Stoney many years ago pointed out that the three principal visual lines were members of a harmonic series, and the interesting discovery has been since made by Professor Balmer that a more comprehensive law includes both these harmonic members and the rest of the series. Thus the hydrogen spectrum appears to present a simplicity not found in the spectrum of any other gas, and therefore it is with great interest that we examine the spectra of the white stars, in which the dark lines of hydrogen are usually strong and broad. In stars of this class we often look in vain for those dark metallic lines so characteristic of other stars which have a nature more nearly resembling our sun.
The question is also discussed as to whether the radiance characteristic of the white stars may be regarded as an indication of an extremely high temperature as compared with that shown by other stars. It seems hardly possible to doubt that such a star as Sirius owes its great lustre not merely to its size, but also to its intrinsic brilliancy, indicative of a high temperature. It may illustrate the attention that has been paid to the spectra of the white stars to refer to some interesting observations of Scheiner; he has found that the objects of this class which are in
