December 17, 1908] 



NATURE 



191 



W^ 



THE STUDY OF STELLAR EVOLUTIOX.^ 

 'E are becoming so accustomed to fresh proofs 

 of Prof. Hale's versatility and thoroughness 

 that the appearance of this volume hardly strikes us as 

 beins so remarkable as it would have done had 

 another written it, but even this fact cannot detract 

 from the feelings of wonder and admiration which are 

 forced upon us as we peruse the contents. 



It should be noted that this work is not a study, 

 but is an account of the study, of stellar evolution, 

 tellini^ us of the methods and apparatus applied in at- 

 tacking the various problems, and how far such means 

 have already been successful. It was at first intended 

 as a handbook to the Yerkes Observatory, but the re- 

 moval of the author to the new solar observatory at 

 Mount Wilson, with its new equipment and newer 

 methods, rendered it advisable that the scope of the 

 work should be widened. 



Prof. Hale looks upon the evolution of stellar systems, 

 not as an entitv, but as a part of the general scheme 

 of evolution which began with the Beginning and at 

 present ends in the social systems which govern man, 

 and it is in this philosophical spirit that he introduces 

 his subject in the first chapter. The great differences 

 between the old and the new astronomy are then 

 pointed out, with reference to the changes introduced 

 by the application of photography to the study of 

 astronomy, and the consequent importance of the 

 methods of reduction which have to be applied to the 

 photographic results. 



The sun is then discussed as a typical star, and 

 Prof. Hale answers a question which is continually 

 being asked by persons who are not thoroughly 

 f.imiliar with solar work. Why at a solar ob- 

 MTvatory, such as Mount Wilson, are time and oppor- 

 I unities 'spent in studying stars and other masses 

 outside the solar system? Why pay attention to those 

 far-away systems w-hich can never, within compre- 

 hensible time, exert anv influence on terrestrial con- 

 ditions? The author expunges all doubt in his reply 

 to these questions. Just as the biologist, by studymg 

 the lower forms of life, discovers the laws which re- 

 gulate the life and being of man, so must the solar 

 physicist appeal to those other stars, of earlier and 

 later birth, in order to comprehend solar phenomena. 

 Those who heard Prof. Hale's evening lecture at the 

 Roval .Astronomical Society in 1905 will recognise the 

 sentiment of the succeeding chapters, in which, whde 

 describing various instruments, he insists upon the 

 useful work that may be accomplished with very 

 modest equipments, and shows that, if the worker 

 only gives earnest consideration to the choice of a de- 

 finite research, he mav find that his smaller instru- 

 ments will prove equally efficient with the larger ones. 

 Among the beautiful full-page illustrations at the end 

 of the volume there are a number illustratmg this 

 |)oint. 



Chapters dealing with the reflecting telescope and 

 the principles of spectrum analysis, in which the work 

 of Hcrschel, Fraunhofer, Kirchhoff, Huggins, Secchi, 

 I.ockver, Janssen, and others is briefly described, bring 

 the history of these subjects up to date, and lead to a 

 description of grating spectroscopes, their history and 

 manufacture. In this regard it is gratifying to be as- 

 sured that Michelson has completed a ruling-machine, 

 with an almost perfect screw, designed to rule i4-inch 

 gratings, and has already completed gratings of ten 

 and twelve inches. By constructing a machine with 



1 " The Study of .Stellar Evolution ; at Account of Some Recent Method 

 of Astrophysical Res-arch." By Prof. George EUery Hale. (The n 



Publications, second series, vol. x.) Pp. xi+252 ; with 104 plate':. (C 



The University of Chicago Press ; London : Wra. Vi'esky and Son, i( 

 Price i6j. 6ii. net. . „ , 



" Populate Astrophvsik." By Dr. J. Schemer. Pp. vi+718 ; 30 Pl- 

 Leipzig and Berlin : B, O. Teubner, tgoS.) Pi 



NO. 2042, VOL. 79] 



t marks. 



four screws he further hopes to reduce the ruling errors 

 to one-fourth the amount produced in a single-screw 

 machine. 



.\fter discussing the phenomena of the sun's sur- 

 face and surroundings, and the historical discoveries 

 concerning them, the author proceeds to a description 

 of the evolution of the photo-spectroheliograph, in 

 which he has played so great a part. He also • em- 

 phasises the point that the explanation of the results 

 offered in this chapter is merely an hypothesis which 

 future researches may modify, and refers to the 

 anomalous-dispersion explanation of Julius as one of 

 the possible alternatives. 



The perusal of chapter xii. leaves us with the ardent 

 desire that British authorities and capitalists would 

 see eye-to-eve w-ith their .American confreres as to the 

 fundamental necessity of fostering scientific work, for 

 Prof. Hale here describes the foundation, equip- 

 ment and work of the Yerkes Observatory. Here, 

 as in other parts of the book, the author strongly in- 

 sists upon the necessity for an equipment capable of 

 undertaking the concurrent study of the correlated 

 solar, stellar, and terrestrial phenomena. 



Notwithstanding the dictum of Newton and the ex- 

 periments of Piazzi Smith and others, the question of 

 the advantage of high altitudes for solar work has only 

 become acute during the last decade or so, and no one is 

 much better qualified than Prof. Hale to discuss this 

 question. It is therefore with interest that we read the 

 chapter dealing with this subject, in which he shows 

 conclusively that altitude alone is not necessarily ad- 

 vantageous. Many of the higher peaks surrounding 

 Mount Wilson have been proved to be unsuitable for 

 solar work, whilst the author's experiences of .Mount 

 Etna, in July, 1894, were not of the kind calculated 

 to make him regard it as an ideal site from which to 

 attempt the photography of the corona without wait- 

 ing for a total eclipse. Mount Hamilton, notwith- 

 standing its glorious night "seeing," is said to be 

 unsuitable for solar work on account of the_ atmo- 

 spheric movements, adverse to good solar definition, 

 set up bv the intensely heated, bare rock which forms 

 the slopes immediately surrounding the summit. 



In chapter xiv. Prof! Hale describes the Mount \MIson 

 site, and, from his experience there, defines five specific 

 requirements for a site to be suitable for the prosecu- 

 tion of solar research and its necessary adjunct, the 

 study of stellar evolution. After describing the Snow 

 telescope and discussing the uses of spectroheliograph 

 plates, the author proceeds to the study of sun-spots, 

 and in this chapter we find one of the strongest argu- 

 ments possible for the inclusion in a solar physics 

 observatory equipment of the apparatus necessary for 

 the correlated study of terrestrial spectroscopy and 

 similar work. Prof'. Hale, has just previously described 

 the numerous pieces of apparatus fitted up, ready for 

 instant use, in the spectroscopic laboratory, and, speak- 

 ing of the powerful magnet used to produce the 

 Zeeman effect, he says :— " It is not a question here 

 of detecting magnetic phenomena in the sun, since 

 most careful study has not revealed any evidence of 

 solar magnetic fields capable of affecting the appear- 

 ance of spectral lines." Yet quite recently, since the 

 above statement was penned, he has published results 

 (N.4TURE, -August 20, No. 2025, p. 369) which strongly 

 suggest that" the Zeeman effect, or something which 

 produces similar phenomena, is en evidence in the 

 sun-spot spectrum ! , 



A chapter on stellar temperatures follows, and in 

 describing the apparatus which has been used in the 

 attempts to measure the stellar heat radiation directly, 

 the author gives some interesting data illustrating the 

 extreme delicacv of the apparatus with which Nichols, 

 working at the'Yerkes Observatory in 1898 and 1900, 



