SPECTRUM ANALYSIS.* IN the whole history of science there is
nothing more wonderful than the discovery or invention (it would be difficult to say which is the more correct term) of spectrum analysis, and the sudden advance of the new method of research into a foremost position a mong all the modes of scientific inquiry. If we take up at random any recent scientific work, whether on astronomy, or chemistry, or meteorology, —nay, even though it treat of subjects like entomo- logy, botany, and conchology, which seem as far as possible re- moved from optical problems,—we cannot tun over its pages without finding more or less copious reference to the prismatic analysis of light. Yet thirteen years ago spectrum analysis bad no existence whatever as a mode of scientific inquiry. It was a subject for research, not a method of research, and there were not a few who regarded it as a subject altogether intractable, while scarcely any believed that it would become the means of advancing our knowledge to any important extent. An eminent physicist wrote thus respecting the peculiarities which had been detected in the rainbow-tinted streak called the spectrum :—" In quitting the mere phenomena of luminous spectra, and rising to the inquiry as to their cause, we enter a more arduous course. The phenomena defy all attempts hitherto made to reduce them within empirical laws, and no complete explanation or theory of them is possible. All that theory can be expected to do is this,—it may explain how dark lines of any sort may arise within the spectrum."
The history of the sudden advance of this great problem into the position of a great solver of problems is full of interest. Not five years had passed from the day when Kirchhoff announced the true meaning of the dark lines in the solar spectrum, before Huggins and Miller were telling astronomers of the terrestrial elements existing in the stars. Then the great secret of the gaaecus nebula) was revealed by Huggins, and soon after the struc- ture cf esmets began to be interpreted. Nor had chemists been idle in the meantime. In 1861 Bunsen and Crookes, by means of the new analysis, had detected three hitherto unknown elements, uesium, rubidium, and thallium, and in 1863 Reich and Richter nad discovered a fourth new element, indium. The importance af the new mode of research in all problems of chemical analysis, as a delicate test for determining the presence of poisons, as a .3mans of improving 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 colouring-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 un- able 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.
• Spectrum Analysis, in its Application to Terrestrial Substances and the Physical Con- atilution of the Heavenly Bodies. fainiliarly explained. By Dr. H. Sehellen. Trans- lated by Jane and Caroline Lassen. Edited, with Notes, by Dr. W. Huggins, LL.D., 41e. London: Longmans and Co. 1872.
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 chap- ters 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 power- ful mode of scientific research yet devised by man. The work of the telescope or of the microscope all men can at once under- stand, 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, everyone 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 inter- pretation 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 por- tions 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 occu- pied 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 fullness of detail, and illus- trated by a fine series of drawings. The coloured platers, representing the prominences as seen by Zollner, Respighi, and Young, are especially interesting and suggestive, more particu- larly 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 in- stead of showing how many thousands of miles would correspond to the height of the coloured prominences, his scale tells us how many globes as large as our earth could be placed one above another, so as barely to reach to the summit of the solar flames.
We are inclined to question whether Schellen's explanation of the method by which the prominences are seen in full daylight will commend itself to the general reader, either as respects dis- tinctness or simplicity. He fails to indicate sufficiently the salient points of the method, and the reader's attention is diverted too often to matters which are of no essential importance. Half the explanation actually given would have been altogether more effective than the whole ; and for a similar reason some of the figures of instrumental arrangements would have been better omitted. We may, indeed, notice in passing that pictures of complicated instruments are altogether out of place in popular treatises. They convey no new knowledge to the initiated, and are utterly unmeaning to the general reader, on whom, moreover, they exercise a deterrent effect. We fancy that many a treatise on science has been closed with alarm by readers who have mis- takenly imagined that the complicated contrivances therein pic- tured must be thoroughly understood (else why introduced at all?) before the subject can be mastered.
The sections on the stars and nebulm are full of interest, though Dr. Schellen is disposed to place somewhat more reliance on the researches of F. Secehi into the stellar spectra than is entertained by our leading spectroscopists. On dealing with meteors and their spectra Dr. Schenen lays a well-deserved stress on the labours of Schiaparelli, to whom science owes the recogni- tion of the strange fact that meteoric rings are associated with comets. Nearly ten years have passed since Schiaparelli an- nounced that "the comet of 1862, No. III." (a large and bright object) "is no other than the remains of the comet out of which the meteoric ring of the 10th of August has been formed in the course of time." Received with doubt for many months, this bold assertion gradually commended itself more and more to the attention of those who studied meteoric phenomena, until in 1866 the recognition of a corresponding agreement between the Novem- ber meteor-ring and Temple's comet of that year removed all doubt as to the reality of the relation. On February 9 of the present year, the gold medal of the Astronomical Society was awarded to Schiaparelli in recognition of this important contribu- tion to our knowledge.
The editorial work of Dr. Huggins adds considerably to the value of Schellen's treatise. In places, the author apportions somewhat incorrectly the merit due to various workers in the field of spectro- scopic research ; so that some of the notes in which Dr. Huggins refers to these points are, in reality, very necessary. But the work of the editor is yet more important in removing errors and explaining difficulties relating to scientific details.
The translators have accomplished their task, on the whole, very fairly. We have noticed some sentences which are ambiguous simply because they are too faithfully translated. It should be remembered that to render in English the meaning of a German writer, it is often absolutely necessary to reconstruct his sentences. For want of such reconstruction, a few of the longer sentences in the present work, though perfectly unmistakable in the original, will be found to admit of two or three different interpretations. In future editions this defect will doubtless be remedied.
Previous page
