proving many processes of manufacture, and as an aid in almost every branch of scientific inquiry, became each year more clearly recognized. We have seen Sorby analyzing by its means the coloring-matter of plants, and the entomologist comparing the spectrum of the glow-worm and the fire-fly, or discussing the absorption-bands peculiar to the fluids of insects. The microscopist employs the powers of the new analysis to solve problems which the magnifying powers of his instruments would be altogether unable to cope with. Nothing, in fine, seems too vast or too minute, too distant or too near at hand, for this wonderful instrument of research, which deals as readily with the mass of Sirius, a thousand times larger and a million times farther away than our sun, as with the ten-thousandth part of a grain of matter in a flame within a few inches of the spectroscopic tube. It is, perhaps, not the least wonderful circumstance about the new analysis that it has already been made the subject of many volumes of scientific lore. A goodly library might be filled with the printed matter which has been devoted to spectroscopic analysis, either in works definitely directed to the subject, or else in chapters set apart for its treatment in works on other subjects. But the general public has undoubtedly not had occasion to complain, as yet, that the analysis has been too fully expounded to them. It cannot be denied, indeed, that hitherto the vaguest possible ideas have been entertained by many respecting the most powerful mode of scientific research yet devised by man. The work of the telescope or of the microscope all men can at once understand, even though the principles on which these instruments are constructed may not be thoroughly understood save by a few. But the case is very different with the work of the spectroscope. When the astronomer says that with a telescope magnifying so many times he can see such and such features in Mars or Venus or Jupiter, every one knows what he means; but, when the spectroscopist says that his instrument shows certain bright lines in the spectrum of a nebula, or certain dark lines in the spectrum of a planet, the general reader has to accept on trust the interpretation placed on such results by the observer.
It was to remove this difficulty that the present volume was originally written. Of its value in this respect we can have no higher evidence than the fact that Dr. Huggins named it to the two ladies who have translated the present edition 'as the best elementary work on spectrum analysis.' The translators—the Misses Lassell (daughters of the eminent astronomer who has just vacated the presidential chair of the Astronomical Society)—remark that the interest they derived from the perusal of this work 'suggested the idea of undertaking its translation.' Dr. Huggins agreed to edit the volume; and, accordingly, we find appended to the valuable text of Dr. Schellen many important (in some cases absolutely indispensable) notes by the English master of the subject.
The work thus translated is from the second German edition, which is not only much larger than the first, but is improved by the correction or omission of several faulty passages. It consists of three parts. The first describes the various artificial sources of high degrees of heat and light. The second relates to the application of the analysis to terrestrial substances. These portions of the work are extremely important, and, on the whole, they are well arranged; but, to say the truth, they are rather dry. Fortunately for the general reader, they occupy together little more than one-third part of the work, the remainder being occupied by the description of the application of spectrum analysis to the heavenly bodies. In this, the third section of the book, we have four hundred pages full of the most interesting matter. The investigations of astronomers into the nature of the sun's globe, and of those wonderful envelopes which surround him, are described with great fulness of detail, and illustrated by a fine series of drawings. The colored plates, representing the prominences as seen by Zöllner, Respighi, and Young, are especially interesting and suggestive, more particularly when the reader's attention has been directed to the scale of miles—or rather of thousands of miles—placed under each. Respighi, indeed, rejects mile-measurement altogether, and can be satisfied only by a scale of terrestrial diameters; so that, instead of showing how many thousands of
