490 



NATURE 



[June 17, 1920 



prevented an adequate representation of all the 

 details of the nebula (Fig. 5). This col- 

 lection of illustrations, showing the forms 

 assumed by the planetary nebulae, will throw 

 considerable light upon the structure and life- 

 history of these bodies. An important addition 

 to the illustrations is that the exposure for record- 

 ing a selected portion of the Orion nebula has 

 been used as a standard, and the time necessary 

 for recording the brightest portion of a planetary 

 nebula is given in relation to that standard. Thus 



It is concluded, therefore, that these giants may 

 be in the Galaxy, but the nearest to us, and, 

 therefore, would only appear outside, and he 

 suggests their inclusion in parallax programmes, 

 as many of them have central stars sufficiently 

 bright for that purpose. 



Further reference cannot be made here to this 

 interesting paper except to add that the author 

 classifies the planetary nebulae according to their 

 appearances, and then discusses these forms in 

 relation to homogeneous oblate spheroidal or 



N.G.C. 



4826 



an approximation to the relative brightness of the 

 planetary nebulae is secured. 



With regard to the distribution of these nebulae 

 in space, an interesting diagram of which is given, 

 Mr. Curtis finds that the smallest objects are 

 almost invariably in, or very close to, the Milky 

 Way, while the larger ptanetaries, "the giants of 

 the class," somewhat more frequent in the 

 vicinity of the galactic plane, are, "on the whole, 

 fairly uniformly distributed over the entire sky." 

 NO. 2642, VOL. 105] 



Fig. 3. — Spiral nebulae mRking a much greater angle with the 

 line of sight, showing clear-cut dark lanes (2903, 4212), and a 

 lane absolutely black and cutting across a whorl at the 

 right end (4826). (H. D. Curtis.) 



homogeneous truncated spheroidal shells under 

 various conditions. 



Prof. W. W. Campbell and Mr. J. H. Moore 

 are the authors of part iv., which is devoted to 

 the spectrographic velocities of the bright-line 

 nebulae (pp. 77-183). The observations are a 

 combination of those made with the 36-in. 



