842 



NATURE 



[February 24, 192 1 



times in which the subjects dealt with lived, in order 

 to show the relation of discovery in physical science 

 to the progress of civilisation. 



A SOMEWHAT novel way of keeping a book up to 

 date, other than by issuing new editions, has been 

 <ievised by the Cambridge University Press, which 

 has projected a series of monographs intended to 

 serve as supplements to Dr. Norman R. Campbell's 

 " Modern Electrical Theory." The series will be 

 edited by Dr. Campbell, who, however, will not write 

 all the volumes. The first three monographs will 

 deal with spectra, the quantum theory, arid the con- 

 stitution of atoms and molecules. It is proposed that 

 the series shall correspond roughly with the chapters 

 of the original book, and eventually supersede the 

 latter. 



Announcement is made of the amalgamation of 

 the firms of Messrs. John Wheldon and Co., of 

 38 Great Queen Street, Kingsway, VV.C.2, and 



Messrs. William Wesley and Son, of 28 Essex Street, 

 Strand, W.C.2. Both firms are well known in the 

 world of science as booksellers and publishers of 

 repute. The business of John Wheldon was estab- 

 lished in 1844, and was concerned mainly with 

 supplying collectors and institutions with scientific 

 works ; recently it has developed in the direction of 

 economic and applied natural science. Of particular 

 value to the new firm will be the collection of scientific 

 journals held by John Wheldon and Co. The business 

 of William Wesley and Son was established in 1855, 

 and dealt similarly with books and journals of science. 

 A valuable side of the firm's activities, which will be 

 continued by the new company, is the numerous 

 agencies which are held for the sale of publications 

 of foreign and Colonial Governments and societies. 

 The establishments will be carried on in future in the 

 name of Messrs. Wheldon and Wesley, Ltd., under 

 the guidance of Mr. H. K. Swann and Mr. E. F. 

 Weslev, who have been managers and proprietors of 

 their respective firms for a number of years. 



Our Astronomical Column. 



A Study of the Stars of Type N. — The stars of 

 type N (Secchi's fourth type) are of great interest; 

 they were formerly supposed to be near the end of 

 their career as suns. However, their concentration 

 in the galaxy is a proof of great distance, and shows 

 that they are in the giant stage. Lick Observatory 

 Bulletin No. 329 contains a photographic study of 

 the spectra of two bright stars of the class, 152 Schjel- 

 lerup and 19 Piscium, by C. D. Shand. Lines in 

 these spectra are very numerous, which increases the 

 difficulty of identification. The presence of carbon, 

 hydrogen, iron, titanium, vanadium, chromium, 

 sodium, manganese, calcium, scandium, and yttrium 

 is certain ; four other elements are suspected. It is 

 difficult to decide whether apparent bright lines are 

 really emission lines or mere spaces between absorp- 

 tion lines; the author inclines to the former view. 



The most striking feature of the spectra is the 

 " Swan " carbon spectrum ; the cyanogen bands are 

 also prominent, and possibly carbon monoxide is 

 indicated. The suggestion is made that the oxygen 

 present may all combine with carbon, thus explaining 

 the absence of titanium oxide, which is prominent in 

 the M stars. 



Many of the N stars are variable, resembling in this 

 point the Md stars. It was formerly suggested that 

 the variability of these faint red stars is due to in- 

 cipient crust formation, which caused accumulation of 

 heat within, leading after a time to the melting of 

 the obstruction. However, the discovery that these 

 stars belong to the giant class renders the crust theory 

 unlikely. Dr. Merrill recently suggested an alterna- 

 tive ; he postulates a veil of blue smoke above the 

 photospheres of these stars, producing almost complete 

 absorption of the shorter waves, and also to some 

 extent obstructing the longer heat-rays. An accumula- 

 tion of heat results which may suffice to vaporise the 

 occulting clouds of carbon, so that a temporary 

 increase of light occurs. 



Spectral changes at various stages of the cycle are 

 discussed. The bright hydrogen lines are most intense 

 at maximum and practically absent at minimum, at 

 which time the carbon absorption becomes stronger. 



NO. 2678, VOL. 106] 



These changes are closely analogous to those in the 

 Md stars. 



The Madrid Observatory. — The Anuario of the 

 Madrid Observatory, 1921, in addition to the usual 

 tabular astronomical data, contains full details of 

 sun-spots and prominences during 19 19, with dia- 

 grams of remarkable prominences, including the great 

 May one seen during the total eclipse^. There is also 

 an article on the spectrum of Nova Cygni 1920 by 

 P. Carrasco. Spectra, photographed at Madrid en 

 nineteen days between .August 23 and September 2c), 

 are reproduced in a manner making it easy to tra< e 

 the progressive changes. There is a full table of 

 wave-lengths of lines, with probable origin, and com- 

 parison with the spectra of o Cygni and j8 Orionis. 

 The earliest spectra (August 23-24) are almost purely 

 absorption spectra. The bright bands are traceable on 

 August 25 and conspicuous from August 27 onwards. 

 The volume also contains the meteorological observa- 

 tions made at Madrid Observatory in 1919. 



Popular Astronomy in Sweden. — Popular Astro- 

 notnisk Tidskrift is an attractive and well-illustrattd 

 periodical the publication of which was commenced 

 last year bv the Swedish Astronomical Society under 

 the editorship of S. .\rrhenius, K. Bohlin, N. V. E. 

 Nordenmark, and H. von Zeipel. The articles in 

 Hiifte 3-4 deal with Nova Aquilse, the moving cluster 

 of the Hyades (for which a parallax of 0027' is 

 found), and Dr. Harlow Shapley's work on the 

 globular clusters. Mr. Nils Tamm contributes an 

 illustrated article on the Kvistaberg Observatory ; the 

 work during 1920 included studies of Mars, Jupiter, 

 Saturn, nebular photography, and magnitude deter- 

 minations of Nova Cygni. Mt. Gyllenskold repro- 

 duces several pictures of auroral streamers, including 

 some interesting photographs obtained at Bossekop, 

 Lapland, in 1910. Some artificial aurorae obtained by 

 Birkeland by cathode rays are illustrated, and the 

 forms deduced from his theory are discussed and 

 shown to agree very closely with the streamers of the 

 solar corona in the crUnse of 1901, 



