LITERARY NOTICES. 



117 



*rum analysis, and certainly the beginning 

 of its utilization as a powerful method of 

 investigation. 



The third part of the book, the most im- 

 portant in extent and results, is devoted to 

 the application of the spectrum analysis to 

 the heavenly bodies. 



The sunlight, according to its bright- 

 ness 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 ; there- 

 fore the author has illustrated the descrip- 

 tion 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 Angstrom, in which the Frauenhofer lines 

 from a to Hi H 2 are coordinated according 

 to their wave-lengths. The accuracy of 

 these lithographic plates is really wonderful ; 

 they will have the great merit of introduc- 

 ing among physicists and astronomers the 

 wave-length scale for the designation of 

 lines instead of KirchhofFs 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 

 Angstrom'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 KirchhofFs and 

 Angstrom'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 ev- 

 ery one the responsibility of his own ideas 

 on this subject. 



The remaining part of the book is en- 

 tirely devoted to the most delicate applica- 

 tions of spectrum analysis to astronomy. A 

 preliminary description of the sun-spots, 

 faculse, and other peculiarities of the sur- 

 face 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 diffi- 



culties 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 fac- 

 similes give the best idea of the phenomena, 

 and show the improvements due to pho- 

 tography and spectroscopy ; the relatively 

 great extent devoted to this account is justi- 

 fied by the importance of the subject ; the 

 spectrum analysis of the prominences is in 

 fact one of the most considerable results ob- 

 tained for a long time in the science of cos- 

 mogony. 



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 atten- 

 tion of astronomers to this subject, though 

 a good number of his assertions may be in- 

 correct. After him, Fizeau, a French phys- 

 icist, 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 mo- 

 tion 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 SecchL 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 unques- 

 tionably 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 

 Fline. 



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 



