# Popular Science Monthly/Volume 48/February 1896/Scientific Literature

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SPECIAL BOOKS.
The world is always conscious of an addition to its intellectual wealth when a leader in original scientific work writes a book. Men like to hear from the masters, especially when they speak, as Prof. Young does, a language that inspires while it instructs. When the first edition of this uniquely interesting book was put forth in 1881 a warm welcome awaited it, not only from astronomers who were eager to learn what one of the foremost investigators of solar phenomena had to say about the sun, but from all readers who take pleasure in seeing the literary powers of our mother tongue turned to useful account in the presentation of the facts of science. And the welcome grew as the circle of the book's readers rapidly widened. No volume of the International Scientific Series has proved more continuously popular.
But the fourteen years that have elapsed since the first appearance of Prof. Young's book have witnessed remarkable advances in astronomy, and particularly with regard to our knowledge of the sun. For a time it was possible to keep the book up to date by notes and appendices to its successive editions. At length this method of revision no longer sufficed, and the author undertook a thorough rehandling of the work, involving the rewriting of considerable portions, and the addition in the text of much that was needed "to make the book fairly representative of the solar science of to-day." That in its revised form it now answers the above definition, quoted from the author's new preface, no one who knows Prof. Young's habitual caution and precision of statement will doubt.
No authoritative utterance concerning a progressive branch of science ​ever came more opportunely than this new edition of The Sun. Within the past few years discovery has followed discovery, and theory has obscured theory in solar physics so rapidly that the general reader, desirous to keep on safe ground, has found himself in a more or less uncomfortable position. One authority, of great weight, has been telling him that the "faculæ" and the "prominences" are identical phenomena; another authority, of perhaps equal weight, has assured him that this is not so. Likewise, in regard to the most interesting question of the connection of sun spots with terrestrial magnetism: on the one hand stand positive assertions of an intimate relationship of that kind, and on the other hand stands Lord Kelvin with his dictum—and the dicta of Kelvin in science have frequently been deemed of equal weight to those of Lord Coke in law—asserting that "we may be forced to conclude that the supposed connection between magnetic storms and sun spots is unreal, and that the seeming agreement between the periods has been a mere coincidence."
Then there have been new theories of sun-spots, new determinations of the solar parallax, new identifications of elements in the sun, the wonderful work of Langley on the infra-red portion of the spectrum, the questions raised by Lockyer's theory of the "dissociation" of elements in the sun, the question of the existence of oxygen in the solar atmosphere, the question whether the sun-spots are really depressions, and many other new and puzzling things, the most surprising of all being, perhaps, the discovery in a Norwegian mineral of "helium," an element which had been found in the sun as long ago as 1868, but the presence of which on the earth had never been detected.
Amid such a confusion the unprofessional wayfarer in science needs a guiding hand, and that is what Prof. Young now most seasonably offers. There is a fairness, a power of discrimination, and a judicial balance in our author's treatment of vexed questions that must create in the reader's mind both confidence and admiration. His brief, shrewd reply to the remark of Lord Kelvin, quoted above, concerning sun-spots and magnetic storms, will find many highly interested readers, and it is made all the more attractive by the vista of possible future discovery which it opens with the suggestion that "it is not perhaps outside the limits of possibility that both the solar and terrestrial disturbance have a common origin in some invasion of power or matter from outer space—that the solar tumult is the brother, and not the father, of our own aurora."
Prof. Young's discussion of Helium, its Identification and Properties, is, of course, luminous and informing in the highest degree. Nothing can be more pleasing than to note the manner in which an unexpected discovery, full of momentous consequences for the work with which he is identified, is received, assimilated, and irradiated by the mind of a leader in science.
Among the new matters treated, one of the most interesting, because it relates to hoped-for advances in the future, is the effort to render the corona visible when the sun is not eclipsed. It is certainly encouraging to know that to Prof. Young "the case appears by no means absolutely hopeless." When we remember the advance in our knowledge of the prominences following Janssen's and Lockyer's discovery in 1868, that those phenomena could be rendered visible with the spectroscope in ordinary daylight, and consider the ignorance that probably would have prevailed ​concerning them if they had remained unseen except during-eclipses, we can echo our author's opinion that success in revealing the mysterious corona in a similar manner "is certainly devoutly to be desired."
Prof. Young has so long been a conspicuous and brilliant figure in the field of spectroscopic investigation that one naturally turns to his revised chapter on The Spectroscope and the Solar Spectrum with pleasing anticipations which are not disappointed. The results of the immense work accomplished in the last decade are here ranged in order with an expert hand, and the remaining gaps in the line of acquired knowledge are made clearly apparent. The list of elements known to exist in the sun has been largely extended in the past few years, but still many that go to constitute a great portion of the crust of the earth have not been recognized in the solar spectrum. Why are they absent? Is it simply a failure to show themselves, or do they not exist there at all? Prof. Young indicates his preference for the view that the missing elements are not really absent from the sun. but only nonapparent, although he points out that the answer to the question is not easy. And then he goes on to marshal some most interesting facts and considerations relative to this subject, and discusses briefly but luminously such topics as the multiple spectra of certain elements, Lockyer's revival of the old "pantogen" speculation and his theory of "basic lines" common to the spectra of different substances, the later work on the question of solar oxygen, etc.
While this book is a record of facts and achievements rather than of theories and attempts at the interpretation of mysteries, yet the great questions still remaining to be answered are, of course, discussed, and in a masterly manner. A fine instance of the author's method of dealing with such subjects is shown in the chapter on The Sun's Light and Heat, where he succinctly reviews questions like these: "How is the sun's heat maintained?" "How long has it lasted already?" "How long will it continue?" "Are there any signs of either increase or diminution?" It is undoubtedly true, as Prof. Young remarks, that to such questions, "in the present state of science, only somewhat vague and unsatisfactory replies are possible," yet they are questions the replies to which, however incomplete, will always command deep interest. And if the facts and speculations accumulated since 1881 have not thrown much light upon these subjects, something has been gained in a clearer comprehension of both the strength and the weakness of prevailing theories. Those are pregnant sentences, for instance, in which, after pointing out the objections to the late Dr. Siemens's theory of the sun, he remarks: "And yet one almost regrets that the theory can not be accepted, for it would remove very serious difficulties that now embarrass the problem of the evolution of our planetary system. The accepted contraction theory of Helmholtz certainly appears to allow too little time for the sun's lifetime of radiant activity to be consistent with a reasonable explanation of the process by which the present state of things has come about."
In briefly summarizing the principal additions noted in the new edition the following may be particularly mentioned: The latest work on the solar parallax, including Newcomb's results and the observations on the minor planets Victoria and Sappho; accounts of all recent advances and discoveries in solar spectroscopy and spectro-photography, including the work of Hale, Deslandres, Dunér, etc.; a statement of the latest accredited theories ​concerning sun spots, such as Schæberle's and Oppolzer's, and an account of Dunér's and the author's work on sun-spot spectra; a summary of recent progress in prominence photography, etc.; facts and conclusions concerning the corona, based on recent eclipses; an account of Langley's infra-red spectrum investigation, and of the work of De Chatelier, Wilson, Gray, and Scheiner on solar radiation and temperature; and, finally, a most interesting supplementary note, already mentioned, on Helium. The size of the volume has been increased by nearly thirty pages, and the number of illustrations has been raised from eighty-two to one hundred.
The Sun, in its new form, certainly deserves, and will unquestionably obtain, an even greater circulation than that which it has hitherto enjoyed.
"Live" natural history is what Prof. Miall would lead the young naturalist to. While he has no disparagement for systematic zoölogy, he wishes to revive an interest in the writings of Swammerdam, Réaumur, Lyonnet, and De Geer, and to promote that observation of the structure and habits of living animals which those authors pursued with most profitable results. In so doing, he is only restoring a balance that has been disturbed of late years. It is certainly an attractive field into which our author invites the amateur. Who does not love to follow a stream through its alternations of still deeps and rippling shallows, or to stroll along the shore of the ever-moving sea? Whether one be occupied with sport or science, the movement of the water and the succession of traces of its action upon the land yield no small enhancement of pleasure. Aquatic insects do not form a distinct class. Representatives of eleven orders are described in this book, so that the spice of variety is not wanting in their study. Under the guidance of Prof. Miall one may watch at leisure the swiftly darting whirligig beetle or examine the fine case of instruments of the female gnat (there are no mosquitoes, our author says, in zoölogy). Other insects classed as aquatic, because they pass their larval and pupal stages in water, are drone flies (the oxen-born bees of the ancients), dragon flies, pond-skaters, tube-making caddis-worms, etc.; all are air-breathers in the adult form. A phenomenon which profoundly affects the lives of these creatures is the surface film of water. By curious adaptations they take advantage of its tension, while on the other hand some minute creatures find it a death-trap. The reader must not look for a severely logical arrangement in this book. There is an introduction in which the invasion of the waters by insects, the surface film, live natural history, and other topics are discussed philosophically. Directions for capturing specimens will be found not among the preliminary matter, but on page 114, and there are biographical notes about the old naturalists where the first extended citations from their respective writings occur. In the illustrations sufficient magnifying power has been used to make the organs of the insects readily distinguishable, with the result of giving some of the little creatures a truly formidable appearance.
* ↑ The Sun. By Charles A. Young, Ph. D., LL. D., Professor of Astronomy in Princeton University. New and revised edition. Pp. 363, 12mo. New York: D. Appleton & Co. Price, $2.
* ↑ The Natural History of Aquatic Insects. By L. C. Miall, F. R. S. Pp. 395, 12mo. London and New York: Macmillan & Co. Price, 6s.; $1.75.