The Spectroscope and its Work

Abstract

ALTHOUGH classed as a manual of elementary of science, this little volume will be found to cover a very wide range of the phenomena of spectroscopy. The opening chapters are occupied with the first principles of the undulatory theory, Newton's classic experiments, and the description of a simple spectro-scopic outfit. In chapters iv. and v. the reader is introduced to the various types of emission spectra shown by radiations from various sources, and to the characteristics of absorption, including the solar fraunhoferic and chromospheric spectra. Chapter vi. deals very lucidly with the theoretical principles to be considered in the design of spectroscopic equipment, showing the relation between angular and linear dispersion, purity and resolving power of various dispersive media, &c. Coming next to the application of the spectroscope to definite branches of research, it is shown how, by the aid of large instruments of special design, the spectra of the stars may be studied, revealing their variation in chemical constitution. This naturally leads to the systems of classification which have been proposed to deal with the complex groupings. In describing the fluted structure of the third-type stars, such as α Orionis, it would have been more correct to speak of the maxima of absorption being nearest to the violet instead of saying that the brighter ends were towards the red, as it is usual to regard the heads of flutings as taken for reference to the positions of flutings. It is also perhaps unfortunate for the student that so much space should be given to the old, incomplete, and now little used classifications, while the more comprehensive and natural systems put forward of recent years are discussed in a few lines. The idea suggested on p. 81 that the maxima of the star Mira (o Ceti) are of the nature of a conflagration is scarcely to be recommended, especially when dealing with beginners, as the practically unchanging character of the spectrum of the star (apart from brilliancy) even at maxima precludes the probability of any such chemical changes as must accompany the production of flame.

The Spectroscope and its Work.

By Prof. H. F. Newall. Pp. 163 + viii Plates. (London: Society for Promoting Christian Knowledge, 1910.) Price 2s. 6d.