September 16, 1922J 



NA TURE 



395 



duced as a direct consequence of changed conditions, 

 and he adds, "I do not accept mutations at all, 

 neither as a direct consequence of changed conditions, 

 nor spontaneously, as being sufficiently proven." 

 The writer of the notice regrets that he should have 

 misrepresented Dr. Sirks's opinions. The criticism 

 arose out of passages in chap, xiv., and referred in 

 particular to the confident narration of Tower's 

 alleged discovery of a sensitive period in the life of a 

 beetle, during which its germ-cells could be modified 

 by external conditions. Dr. Sirks summarised the 

 account in a statement which may be translated thus. 

 "In other words : without any doubt Tower suc- 

 ceeded, by means of very abnormal conditions of life, 

 in breeding from the original form Leptinotarsa 

 decemlineata offspring which had lost one hereditary 

 factor ; he called these ' mutants, ' the name which 

 is generally given to forms suddenly arising which 

 exhibit hereditary variations." Nothing could be 

 more explicit. In continuation, however, Dr. Sirks 



definitely dissociates himself from the interpretation 

 of the alleged new forms as mutants. The objection 

 should therefore have been expressed differently. It 

 was not the interpretation which seemed to the 

 reviewer unfortunate or uncritical, but rather the 

 unqualified repetition of sensational reports which, 

 though they have attained some currency, are gravely 

 in need of confirmation. 



Messrs. Benn Bros., Ltd., announce a new series 

 of monographs dealing with gas and fuel. The first 

 three volumes will be " The Administration and 

 Finance of Gas Undertakings, with Special Reference 

 to the Gas Regulation Act, 1920," by G. Evetts ; 

 " Gasworks Recorders," by Dr. L. Levy ; and " Modern 

 Gasworks Chemistry," by Dr. G. Weyman. The 

 same firm will also publish shortly " Practical Optics 

 for the Laboratory and Workshop," by B. K. Johnson, 

 and " The Bronze Age and the Celtic World," by 

 H. J. E. Peake. 



Our Astronomical Column. 



September Meteors. — Though September is not a 

 month in which any rich shower of meteors is periodic- 

 allv visible, a considerable number of meteors and 

 many radiant points of moderate activity should be 

 seen. Fireballs are also particularly abundant during 

 the month, especially on September 13-15, and again 

 on September 24-28. The principal systems of 

 meteors at this time of the vear radiate from Aries, 

 Perseus, Auriga, and other constellations in that part 

 of the heavens. At the middle of September there 

 is usually a strong display of e Perseids from 6i° +36 ; 

 there is also a prominent shower from near a Cygni, 

 at 314° +48 , and swift, streaking meteors from the 

 Lynx frequently manifest themselves. September is, 

 in fact, usually a productive period for the meteoric 

 student, and further watching may reveal a some- 

 what rich annual display that hitherto has not received 

 the notice it merits. 



Invisible Sunspots. — In the year 1908 Dr. G. E. 

 lli!'- published (Contributions from the Mount 

 Wilson Solar Observatory, vol. i., No. 26) his dis- 

 covery of solar vortices. This vortex hypothesis 

 assumes that a sunspot resembles a vast tornado in 

 which electrified particules, due to ionisation in the 

 solar atmosphere, are rapidly whirled. The invariable 

 presence of a magnetic field, caused by the revolving 

 charges, confirmed this view, but it was also sup- 

 ported by other results of observation with the 

 spectrograph and spectroheliograph. It was found 

 also that most sunspots were associated in pairs of 

 opposite magnetic polarity, and 61 and 33 per cent, 

 respectively of 970 spots were observed as bipolar 

 and unipolar. The fact that some groups oscillated 

 between unipolar and bipolar types, one or more 

 small spots appearing and d ; sappearing within the 

 mass of calcium flocculi, suggested to him the idea of 

 looking for invisible spots. That these might be 

 found seemed most probable, there being vortices 

 giving appreciable magnetic fields without any 

 actual visible sunspots. Dr. Hale now describes his 

 recent investigation in this direction (Proc. Nat. 

 Acad, of Sciences, U.S.A., vol. 8, No. 7). The method 

 he adopts is a device for rendering feeble magnetic 

 fields visible by the Zeeman effect, and details of the 

 procedure are given in his paper. Suffice it to say 

 that he has found a great number of cases in which 



NO. 2759, VOL. I 10] 



a local magnetic field was observed where no spot 

 was recorded. He points out the importance of 

 making systematic observations of invisible spots, 

 especially during the periods preceding and follow- 

 ing the visible life of those that reach maturity, 

 in order to assist in revealing the cause of sunspot 

 formation. 



Absolute Magnitudes of Stars. — Several years 

 ago Prof. H. N. Russell produced a striking diagram 

 of absolute magnitudes, on which the theory of giant 

 and dwarf stars was based ; it met at first with some 

 opposition, but has gradually won its way to general 

 acceptance. The number of stars of which trust- 

 worthy parallaxes (photographic, spectroscopic, and 

 hypothetical) have been obtained, has now been 

 greatly increased, and Dr. Heber D. Curtis has pre- 

 pared a revised diagram, which is reproduced in the 

 Journal of the R.A.S. of Canada for July-August. 

 It contains 2375 stars, and shows the division into 

 giants and dwarfs very plainly. The gap between 

 them is complete in type M, but begins to be filled by 

 a few stragglers in type Ko, suggesting that this may 

 be the maximum temperature attained by stars of 

 small mass. In types G and K the giants outnumber 

 the dwarfs, but the reverse holds in type F. The 

 giants here are comparatively few, but they include 

 some of remarkable luminosity. 



Broadly speaking, the regions of maximum fre- 

 quency form two straight lines ; that of the giants 

 forms a horizontal line at magnitude + 1 ; that of 

 the dwarfs slopes downwards from +1 J- at type Ao 

 (the giants and dwarfs being here mingled) through 

 + 5 at type G5 (so that the sun is an average star of 

 its type) down to 8 or 9 for Ma. 



The diagram suggests to Dr. Curtis the conclusion 

 that a sensible number of B-stars have parallaxes of 

 the order of o"-02 ; he notes that stars of this type 

 are being put on the working lists at the Alleghenv 

 and Leander McCormick Observatories. These stars 

 cannot as yet be investigated for parallax bv the 

 spectroscopic method, so that the results of these 

 measures will be awaited with interest. It will be 

 remembered that the results have a bearing on the 

 adopted distances of the globular clusters. The 

 fainter the absolute magnitude found for the average 

 B-star, the nearer we must put the clusters. 



