NA TURK 



)65 



THURSDAY, OCTOBER ii, 1894. 



ASTRONOMICAL SPECTROSCOPY. 



A Treatise on Aslronomical Spectroscopy. A trans- 



I lation of Dr. J. Scheiner's " Die Spectralanalyse der 



M Gestirne." Translated, revised, and enlarged by E. 



" B. Frost, M.A. xiii. + 4S2 pp. Svo., Si woodcuts, 



2 plates. (Boston and London : Ginn and Co., 1S94.) 



THE German original of this work appeared in the 

 autumn of 1890, and was doubtless eagerly wel- 



I comed by many who had felt the w.int of a handbook of 



I spectroscopy which gave a tolerably detailed account of 

 the vast amount of work accumulated during the last 

 twenty-five years. From the position of the author in 

 the Astrophysical Observatory at Potsdam, it was to be 

 expected that the subject would be treated in a scientific 

 spirit, and that he would not merely produce a popular 

 book, but one which would be of real use to students 

 of the youngest branch of astronomy. These expecta- 

 tions were to a great extent fulfilled, although it must 

 have been felt by many readers outside Germany that 

 the book suffered from the same defect as Secchi's '" Le 

 Soleil," that of frequently giving undue prominence to 

 the researches made at the observatory where the author 

 was working. 



The English edition now before us is not a mere trans- 

 lation. Not only has it been brought up to date by the 

 addition of the results of observations published since 



: 1890, and in some cases even by the insertion of results 

 of American work not yet published elsewhere, but 

 Prof. Frost has evidently been anxious to be more fair in 

 dealing with older work of non-German astronomers, ana 

 to bear in mind that all spectroscopic researches do not 



j bear the stamp, " Made in Germany." No attempt has 

 been made to distinguish the portions so added from the 

 original text, except in a few cases where Dr. Scheiner 

 requested it, and where the additional matter is put in 

 brackets. At the end of the preface Dr. Scheiner has 

 inserted a number of notes on various points, as to which 

 he differs from the views of the translator. 

 The first part (i lopp.) deals with "Spectroscopic Appar- 



11 atus," beginning with the effect of imperfect achromatism 

 of the telescope objective on the spectrum, and the means 

 it furnishes of testing the achromatism of an object- 

 i;lass. Harkness, Vogel, and Young have applied this 

 method in various ways ; but it may be mentioned here 

 that the method is much older, and has been used by 

 d'Arrest and others. The next paragraphs discuss the 

 passage of light through prisms and pris:n-systems, the 

 loss of light by reflection and absorption, the curvature of 

 the spectral lines, the properties of the cylindrical lens, 

 and the effect of atmospheric disturbances on spectro- 

 scopic observations. A lengthy account follows of all the 

 various spectroscopes and spectrometers which have 

 been brought into use from about the year 1817 (not 1823), 

 when Fraunhofer designed the objective-prism spectro- 

 scope, and down to the present day, the theories and 

 modes of adjustment of the instruments b^ing fully con- 

 sidered. The translator has here added accounts of 

 Rowland's construction and use of concave gratings, and 

 of Michelson's and Morley's application of interference 

 NO. 1302. VOL. 50] 



methods to spectroscopic measurements ; he might also 

 in this chapter have inserted a description of the 

 bolometric methods of observation, which have yielded 

 such splendid results (they are partly mentioned in the 

 chapter on the sun, but the instrumental arrangements 

 should have been given in detail). In the paragraph 

 on photographic spectra the Potsdam spectrograph is 

 chiefly considered, but the translator also describes 

 Hale's spectroheliograph. 



The second part of the book (pp. 111-150) on " Spec- 

 troscopic Theories" is divided into two chapters on 

 Kirchhoffs Law of the ratio between the absorptive and 

 emissive power, and on Doppler's principle. Prof. 

 Frost states in the preface, that in view of the contra, 

 dictory results of recent investigations upon the emission 

 of light by gases, he has not thought it wise to make any 

 additions to the chapter on Kirchhoffs Law. It seems, 

 however, strange that he should not have drawn atten- 

 tion to these investigations, and pointed out their immense 

 importance for the interpretation of celestial spectro- 

 scopic observations, though a careful reader will not fail 

 to see, even from the short account given of E. Wiede- 

 mann's researches, how great a role "luminescence'' 

 phenomena are likely to play in future theories of the 

 nature of celestial bodies. The chapter on Doppler's 

 principle deals fully with the theoretical aspect of this 

 important matter and the various objections which have 

 been raised from time to time, while the splendid 

 practical results are deferred to a chapter at the end of 

 the book. 



The third and largest part (pp. 151-360) is devoted to 

 the " Results of Spectroscopic Observations." In the 

 German original all wave-lengths were based on the 

 Potsdam system of Miiller and Kempf, and were ex- 

 pressed in millionths of a millimetre, but the translator 

 has reduced them all to Rowland's system of 1893, and 

 has adopted the tenth-metre as his unit, in accordance 

 with the practice of most British and American spectro- 

 scopis's. The chapter on the sun describes first the 

 various methods of investigating the ultra-red spectrum, 

 and includes an account of Langley's unpublished 

 method. By this the invisible spectrum is moved by 

 clockwork across a bolometer strip, the passage of the 

 lines being recorded by a sensitive reflecting galvano- 

 meter, the point of light from which falls on a photo- 

 graphic film, also moved synchronously by clockwork in 

 a direction at right angles to the plane of the mirror's 

 movement, thus automatically producing an energy curve. 

 This is subsequently converted into a linear spectrum 

 containing dark lines corresponding to the cold spaces in 

 the invisible spectrum. The ultra-violet spectrum is next 

 shortly described, and lists of elements present in the 

 sun are given. In the paragraph on the atmospheric 

 lines, the translator has substituted Cornu's list of these 

 for those of Angstrom and Vogel, which Dr. Scheiner 

 had preferred ; but we miss references to Dr. L. 

 Becker's investigation of the low-sun spectrum and 

 (curiously enough) to Dr. Miiller's spectroscopic ob- 

 servations on the Slintis, although the latter were 

 published more than a year and a half ago in the Potsdam 

 publications. More remarkable than these omissions is, 

 however, the brevity with which the spectra of sun-spots, 

 facula:, and the chromosphere arc treated in only twcnty- 



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