192 



NA TURE 



[December 17, 1908 



was able to detect the heat radiations received from 

 Arcturus and N ega. The former was found to send 

 us heat equivalent to that given by a candle about six 

 miles away, if there were no absorption by the 

 atmosphere, and Vega less than half that amount. 



Following a chapter devoted to the nebular hypo- 

 thesis we find a discourse on stellar development, and 

 some interesting points are made concerning the 

 various stellar classifications in the light of recent re- 

 search. For example, Lockyer's temperature classi- 

 fication has been criticised on the ground that the ob- 

 served changes of intensity of stellar lines might be 

 produced by an indeterminate combination of electrical 

 and temperature action. This has been recognised and 

 reiterated by the author of the classification, who 

 accepts the changes, whatever be their cause, as a 

 basis on which a working hj-pothesis might be erected. 

 But now we find Prof. Hale writing to the effect that 

 the results obtained in the Mount Wilson laboratory 

 imitation of sun-spot phenomena " seem to favour 

 the view that a temperature classification of the stars, 

 0.1 the basis of the relative intensities of lines, is per- 

 fectly possible." In these experiments all electrical 

 phenomena were excluded, but the above statement is 

 not made unreservedly, as shown in the subsequent 

 discussion of the meteoritic hypothesis: The work 

 with the new 6o-inch reflector at Mount Wilson, it is 

 hoped, will provide a great deal of information 

 respecting the fainter stars which has hitherto not 

 been obtained. 



In dealing with the meteoritic and planetesimal 

 hypotheses. Prof. Hale directs special attention to the 

 outstanding uncertainties respecting the transitional 

 stage, nebula to star, and urges the importance of 

 directing special attention to nebulas by obtaining 

 photographs of their structures and spectra ; this re- 

 search can only prove fruitful if the persistent prosecu- 

 tion of correlated laboratory experiments is carried out 

 concurrently. 



Discussing the question of the variation of the heat 

 received from the sun, the author points out how small 

 an amount of definite measurement has yet been 

 undertaken, and urges that other observatories, in 

 other regions of the earth, should cooperate in the 

 holographic work. 



Kodaikanal, where the dry season corresponds with 

 the wet season in South California, and an Australian 

 station are suggested as localities in which the ob- 

 servations might be profitably inaugurated. 



The importance of active cooperation between solar 

 and meteorological observers, such as has of late years 

 been instituted by the International Commission, is 

 also emphasised. 



The concluding three chapters (xxiii.-.xxv.) are 

 essentially of general interest. In the first the author 

 describes at some length the making of the 6o-inch 

 reflector by Ritchey in the Mount Wilson workshops 

 (Pasadena), and illustrations of the process are to be 

 found among the plates. Then some possibilities of 

 new instruments, e.g. the loo-inch reflector now 

 under construction, are reviewed, and in the final 

 chapter warm encouragement is given to the amateur 

 observer. This embodies a series of hints on fitting 

 up instruments, and, coming from a master who com- 

 menced his far-reaching studies with home-made in- 

 struments, they should be especially welcome, as thev 

 re essentially practical. 



The printing and general get-up of the volume are 

 1 the high order one is accustomed to expect from 

 tiie Chicago University Press, and the 104 full-page 

 reproductions of actual photographs, which are bound 

 up at the end, form by far the finest collection of 

 general astronomical pictures ever vet published in a 

 single vokime. 



XO. 2042, VOL. 79] 



In Prof. Scheiner's book we have a more conven- 

 tional treatment of the subject of astrophysics, in 

 which, in two parts, the whole subject is discussed 

 under the customary headings and in popular termin- 

 ology. Thus in the first section of part i. we find 

 simple explanations of the fundamental principles 

 underlying the methods employed, such as those of 

 refraction, reflection, polarisation and dispersion of 

 light, and the capacity and psychophysiological action 

 of the eye considered as the final instrument on which 

 the interpretation of all the phenomena depends to so 

 large an extent. 



In the following section the specific instruments 

 are described, and the construction and adjustments 

 of the spectroscope are expounded at length. The de- 

 termination of absolute wave-lengths introduces us to 

 the principles underlying the employment of the 

 grating, and to the work of Kirchhoff, Doppler, 

 Zeeman, and other pioneers in spectroscopic research. 



The discussion of the spectra of elements is inter- 

 polated with data, such as the relationships of the 

 spectra to the element's position in the periodic 

 system, which should prove valuable for reference. 



Photometry forms the subject of section iv., and 

 the student should find helpful the descriptions and 

 illustrations of the various instruments, and the dis- 

 cussion of the psychophysical actions which have to 

 be accounted for in performing the reductions. The 

 uncertainty which still attaches to the results obtained 

 from attempts to measure the solar heat radiations is 

 discussed in a brief chapter, and is well illustrated by 

 a tabulated statement of the values derived for the 

 solar constant by the various observers from Pouillet 

 ih \%xi to the author in 1902 ; the values range from 

 1.7 to 3.4 gr. cals., the lowest having been obtained 

 by Vallot in 1896, and the highest by Crova and 

 llansk)' in 1S97. 



The four chapters which bring the first part of the 

 book to a conclusion deal with the application of photo- 

 graphy to astronomical work, and so much has already 

 been written about the subject that there is but little 

 new matter for the author to expound ; but the instru- 

 ments are clearly described and their various func- 

 tions explained, the matter in the text being well illus- 

 trated by figures. 



In eleven chapters (xviii.-xxviii.), the second part of 

 the book deals with the results obtained from the em- 

 ployment of the instruments and methods previously 

 described. The various solar phenomena, the surface 

 appearance and physical characteristics of the moon 

 and planets, and the results obtained from observa- 

 tions of comets and the zodiacal light are expounded 

 at some length, and are illustrated by drawings and 

 photographs in the text. These figures are generally 

 good, but it is a pity that the drawings of several 

 features, such as the Martian surface and the in- 

 tensified lines of sun-spot spectra, could not have been 

 supplemented by some of the excellent photographs 

 now obtainable. 



Chapter xxiii. deals with the subject of nebula, and 

 includes a useful table of nearly eighty N.G.C. 

 nebulas which have been shown certainly to be 

 gaseous ; the equatorial coordinates of these objects 

 for igoo are given, and a striking feature of the list is 

 the great preponderance of planetary nebulas. In the 

 description of the physical characters, the distances, 

 motions and extent of these gaseous masses, various 

 tables of data are interpolated, and should facilitate 

 references to the subject. One of exceptional interest 

 is that in which the determined radial-velocities of 

 thirteen nebulae are shown. Taking mean values, we 

 see that the extremes of approach and recession are 

 -65 and -1-44 km. per sec, the values obtained for 

 X.G.C. 6543 and 6790 respectively. 



