Popular Science Monthly/Volume 2/November 1872/Literary Notices
Spectrum Analysis in its Application to Terrestrial Substances, and the Physical Constitution of the Heavenly Bodies. By Dr. H. Schellen. D. Appleton & Co., 1872.
The following able notice of Dr. Schellen's book is abridged from an article in Nature: It is not difficult to deliver interesting lectures or to write an instructive book on spectrum analysis. The rapid succession of brilliant discoveries in this new branch of science, the amount of fundamental facts added by it to human knowledge, especially in the field of the cosmical world, assure the lecturer or writer, appealing to the intelligent but not scientific public, of useful and legitimate success. But what is not so easy to do is, to interest at the same time gens du monde and scientific men, by offering a selection of the most recent discoveries in a bright and literary form attractive to the former, and yet keeping for the latter the appearance of precision, and exactness of the numerical results. All these conditions are very happily filled in "Schellen's Spectrum Analysis," edited by Mr. W. Huggins from the second German edition.
The first part, introductory, is occupied by a description of the artificial sources of high degrees of heat and light, of which the study is so intimately connected with the chemical and astronomical phenomena embraced in the field of spectrum analysis; various apparatus, for instance, the gas-burner, the magnesium lamp, the Drummond lime-light, the electric spark of the induction coil, the Geissler's tube, and the electric light produced by voltaic batteries, are described, and the practical adjustments are briefly but sufficiently referred to for a good understanding of the subject.
The second part is devoted to an elementary abstract of the geometrical and mechanical properties of light. The fundamental analogy between light and sound is developed, in order to explain to a reader unlearned in optics how the color of a ray is the corresponding element of the pitch of a musical sound, and how it is possible to define a colored ray by the time of its luminous vibrations. The description of refraction phenomena, especially the paths of rays through a prism, leads naturally to the separating process of the different colors on which spectrum analysis is founded.
A considerable number of chapters is devoted to the construction of the simple and compound spectroscope. The chief points of this construction, especially the contrivances for the simultaneous comparison of two spectra, the determination of the position of lines in the spectrum, are carefully described. Afterward a practical account of the methods for exhibiting spectra of terrestrial substances, for instance, metallic salts volatilized in a gas-burner, etc., will certainly interest chemists.
An interesting chapter contains the theoretical and experimental explanation of the reversal of the spectra of gaseous substances. This phenomenon, studied independently by Foucault and Angstrom, and definitely generalized by Kirchhoff, is perhaps the chief point of the history of spectrum analysis, and certainly the beginning of its utilization as a powerful method of investigation.
The third part of the book, the most important in extent and results, is devoted to the application of the spectrum analysis to the heavenly bodies.
The sunlight, according to its brightness and to the peculiarities of its spectrum, is the best and easiest example to study. The dark lines in infinite number which it shows, called "Frauenhofer lines," from the discoverer, deserve special attention; therefore the author has illustrated the description of the sun-spectrum with two sets of maps. The first is a reduction of Kirchhoff's maps engraved on wood, representing in several tints the lines from A to G; the second series is a reduction to about half size of the admirable normal solar spectrum of Angström, in which the Frauenhofer lines from a to H1 H2 are coordinated according to their wave-lengths. The accuracy of these lithographic plates is really wonderful; they will have the great merit of introducing among physicists and astronomers the wave-length scale for the designation of lines instead of Kirchhoff's scale, which is an arbitrary one; and in any case they will facilitate the transformation of the data from one to another. I must add that Angström's maps have been introduced into the present edition by the English editor, and that such an addition is certainly one of the greatest attractions of this book for scientific men.
A good abstract of Kirchhoff's and Angström's memoirs on the coincidence of the dark solar lines with the bright lines of metallic vapors leads to the hypothetical constitution of the sun; this problem is so difficult, that it is necessary to leave to every one the responsibility of his own ideas on this subject.
The remaining part of the book is entirely devoted to the most delicate applications of spectrum analysis to astronomy. A preliminary description of the sun-spots, faculæ, and other peculiarities of the surface of the sun, of the prominences round the disk, and so on, is given before the spectroscopic process for analyzing these appearances is introduced, and enables the reader to understand very well the difficulties of the problem and the interest of its solution. I must mention especially the interesting account of the three total solar eclipses of 1868, 1869 and 1870. A large series of drawings and photographic facsimiles give the best idea of the phenomena, and show the improvements due to photography and spectroscopy; the relatively great extent devoted to this account is justified by the importance of the subject; the spectrum analysis of the prominences is in fact one of the most considerable results obtained for a long time in the science of cosmogony.
The spectroscope, as it is known, is able to give an exact measurement of the proper velocity of the luminous bodies. A German physicist, Doppler, deserves to be mentioned as the first who called the attention of astronomers to this subject, though a good number of his assertions may be incorrect. After him, Fizeau, a French physicist, to whom we are indebted for the first determinations of the velocity of light on the surface of the earth, showed the errors of Doppler in a little paper not very well known, published in 1849, and calculated the apparent change of refrangibility which would be produced by the proper motion of some heavenly bodies; but no direct experiment was made before the complete application of spectrum analysis to the sidereal phenomena. In this way Schellen's book gives a good abstract of the works of Huggins and Secchi. In these researches the velocity of rotation of the sun was to be tested as a verification of the general law of the phenomenon. I ought to say that the rather discordant results want a theoretical analysis, because the problem seems to me, in the case of the sun, more complicated than it appears at first sight. However, the influence of the velocity of the gas streams, especially of hydrogen, which constitute the greater part of the prominences, is unquestionably verified by Lockyer's observations. In the same way Huggins has proved and determined the proper motion of Sirius by the apparent change of refrangibility of the F line.
The remaining part of the book is devoted to stellar and meteoric spectrum analysis. It is impossible to give a superficial notice of the beautiful researches of Huggins and Secchi, researches which are always going on; the reader will find with interest various important results of these studies—for instance, the existence in many stars of a good number of terrestrial substances—hydrogen, nitrogen, magnesium, sodium, etc.
One of the most interesting facts is the observation of the temporary star which appeared in May, 1866; the great brightness of the star was due, as indicated by the spectroscope, to an immense mass of incandescent hydrogen.
At the end of the work the author gives some very important observations of Huggins and others on the spectrum of nebulæ; the chief result is the possibility, with the aid of the spectroscope, of distinguishing by the composition of their light the true nebulæ from the clusters of stars.
Finally, a description of the spectrum of the aurora borealis, the identification of its bright lines with some bright lines of the solar corona, a description of various meteors, lightnings and their spectra, show into what difficult objects this new branch of science has pushed its investigations.
On the whole, this book must be considered as a good type of a "popular work;" it deserves the attention of the public, and the esteem of scientific men; and, finally, it recommends itself by a gracious side. It was translated into English by two ladies, who have had the double merit of giving a proof of their good scientific taste, and of showing an example of the help which their sex is able to afford to science.
Life in Nature.—Man and his Dwelling-Place. By James Hinton. New York: D. Appleton & Co.
These works are unique in the scientific literature of the present time, and, although treating of different topics, are so characterized by a common spirit and method, that they may properly be considered together. Their author is a London surgeon in busy practice, but who has not permitted the pressure of professional duties to prevent him from giving close attention to the grave questions by which the mind of the age is agitated. Nor is Mr. Hinton a mere amateur who recreates with philosophy; he is a pioneer investigator in the field of science, and has occupied himself much with those new and large dynamical questions, and their various applications, with which scientific philosophers have been so intently engaged during the last quarter of a century. His inquiry into the physical conditions of vegetable growth, showing that it is governed by definite and traceable forces, and takes place in the direction of least resistance, like all mechanical effects, forms an important contribution to biological science, and was arrived at independently by Mr. Hinton and Herbert Spencer. Yet the author of these works has not dedicated himself to any line of special research (although from the fertility of his ideas, and the acuteness and originality of his views, he might, undoubtedly, have done so with eminent success); but, having mastered the more vital and comprehensive principles of modern research, he takes them as the starting-point for still larger views. Science, indeed, in its ordinary acceptation, is not to him an end. Though deeply imbued with its spirit, and equipped with its latest results, he is not satisfied to rest in this sphere of ideas: it is as leading to something beyond, or as furnishing a basis for something higher, that they have to him their principal value. As Bacon holds science subordinate to the ends of utility, and the practical service of humanity, Mr. Hinton would make it subordinate to the unfolding of man's spiritual nature. He prizes science chiefly for its religious uses, or as an interpretation of the divine order of the world. Maintaining the fundamental harmony of all truth, and that religion represents a verity of the universe as much as astronomy, he has taken it as his task to elucidate the harmonies that must prevail among the different aspects of truth in order that religious faith may be grounded in scientific principles. The results of science, and the knowledge we have of man and the external world, are the author's postulates; and from these he aims to pass, by unbroken logic, to the spiritual order of being. Holding Nature to be a sphere divinely designed for man's highest development, he admits no breaks in the order, and insists that the former must be understood before the latter can be determined. Science, therefore, according to Mr. Hinton, is the foundation and prerequisite of man's true spiritual unfolding.
It has been made a criticism of Mr. Hinton's books, that their arguments are not fully sustained; or that, while their first portions are clear and cogent, the latter parts are indefinite and less conclusive. But this criticism, attributes to defect in discussion that which is due to the nature of the subject-matter, for the ideas successively dealt with are so different as almost to appear contrasted. In the sphere of physical Nature, there are a definiteness, a quantitative sharpness, and a kind of tangibleness in the truths established, which disappear as we pass into the domain of moral and religious conceptions. This contrast of the phenomena in the two spheres, which are precisely conceived in the one case and not in the other, has been made the ground for denying that there can be any true science in the higher realm of man's moral and spiritual activity. But the objection is not valid; for, wherever there is an orderly and coherent body of truths, though they cannot be formulated with exactness, there is the legitimate basis of science. It may be long before the reconciliation and unification of unlike ideas and diverse systems of opinion will be completely accomplished; but it is no longer regarded as impossible, and every able attempt to realize it brings us a step nearer to the final and desirable result. Much is said, in these times, of the conflict of science and faith, and many maintain that they are invincibly hostile and must be permanently alienated. Mr. Hinton holds that this is an error due to the incompleteness and imperfection of present knowledge which the advance of thought is certain to correct, and all who read his works must confess that they are able and original contributions to this end.
"Life in Nature," aside from the higher purpose for which it was written, is one of the most charming studies in biology that our language affords. It abounds in interesting facts illustrating the beautiful laws of vital phenomena, and stated with unrivalled clearness, and is marked by keen and original insight into the old obscurities of the subject. The first chapter treats of "Function, and how we act;" the second of "Nutrition, and why we grow." The subsequent chapters take up the "Vital Force and Laws of Form," the "Universality of Life," "The Living World," "The Phenomenal and True," the "Organic and the Inorganic," and "Nature and Man." The volume is neatly illustrated, and we recommend it to all who care either for the strict science of the subject, or for the larger questions to which it leads.
"Man and his Dwelling-Place" was written fifteen years ago, has been recast, condensed, and made to embody the author's maturer views. Its perusal should follow that of "Life in Nature," as it deals with a higher range of questions, and is of a more speculative and metaphysical quality.
Mr. Hinton writes in a lucid, attractive, and eloquent style, and his books contain many passages of remarkable impressiveness and beauty. In the felicity of his delineations he often reminds one of Ruskin; but, unlike the great Rhapsodist of art, he is never run away with by his rhetoric. The intensity of his convictions and the earnestness of his feelings give warmth and force to his language, which is still chastened and restrained by the discipline of refined scholarship.
Intermembral Homologies. The Correspondence of the Anterior and Posterior Limbs of Vertebrates. By Burt G. Wilder, S.B., M. D. Boston, 1871.
Apparatus for Electric Measurement, with Rules and Directions for its Practical application. By L. Bradley. Jersey City, 1872.
Proceedings at the Fifth Annual Meeting of the Free Religious Association. Held in Boston, May 30 and 31, 1872.
Papers relating to the Transit of Venus in 1874, prepared under the Direction of the Commission authorized by Congress, and published by Authority of the Hon. Secretary of the Navy. Washington, 1872.
A Classified Catalogue of the Birds of Canada, including every Species known to visit the Several Provinces which now form the Dominion of Canada. By Alexander Milton Ross. Toronto, 1872.