NOTES. 



ASTRONOMY. 



I'.y A C. D. Crommelin, B.A., D.Sc, F.R.A.S. 



llll DISTRIBU1 CON OF ALGOL-STARS IN SPACE. 



'I Inn- is .hi article mi tins subject in The Astropk} 

 Journal, December, 1914, by II. N Russell and II. Shapley. 

 The s] " gives the masses, ami tin- type <>i spectrum 



also gives the probable surface brilliancy. The absolute 

 magnitude can be deduced with some confidence: this 

 compared with the visual magnitude gives the distance 

 u is estimated that the uncertainty is not more than 

 twenty-five per rent.). The mean parallax of the ninety 

 stars discussed is .,,',-/'. implying a distance of 300 parsecs, 

 or 972 I..V. The mean of the distances, however, comes out 

 as 24001 Y ["he method gives 125 L.Y. for Algol, 109 L.Y. 

 for /j Aurigae. Din 1 1 measures of their parallaxes give 

 67 L.Y. and 95 L.Y. The agreement is tolerably good. 

 \V UrsaeMajoris(164 L.Y.) and R Canis Majoris (180 L.Y.) 

 also seem to lie within a measurable distance, but all the 

 others are very remote. They show a considerable con- 

 centration towards the galactic plane. Thus seventy-five 

 of the ninety stars lie within 30° of this plane — on uniform 

 distribution there would be only forty-five. The same result 

 holds for the linear distances from the galactic plane. 

 The average distance from this plane is about 450 L.Y. 

 The distances have been calculated on the assumption that 

 there is no absorption of light in space. Evidence is accumu- 

 lating that the absorption is sensible but small. Using 

 King's value of the absorption, the three greatest distances 

 of stars from the Sun, which before were given as 17200 L.Y., 

 12400 L.Y., 7900 L.Y., are reduced to 4900, 4200, 3200 

 respectively. The average distance of all the stars dis- 

 cussed from the galactic plane is now reduced to 280 L.Y. 



A similar investigation has been made for the Cepheid 

 variables : this was partly done by Hertzsprung, and has 

 been completed by Russell and Shapley. They prove to 

 be on the average one and a half times the distance of the 

 Algol variables. This is explained by their enormous 

 intrinsic brightness, so that they can be seen at a much 

 greater distance. Both classes of variables agree in in- 

 dicating that our stellar system is comparatively shallow 

 (perhaps not more than 1000 L.Y. in thickness) towards the 

 galactic poles. The median plane of the stellar system 

 appears to be somewhat to the south of the Sun, perhaps 

 some 50 L.Y. distant from it. This is probably the reason 

 of the greater richness of the southern hemisphere in bright 

 stars. 



There are two other articles by H. Shapley in the same 

 magazine. One deals with additional variables in the cluster 

 Messier 3 (in Canes Venatici). S. Bailey had already found 

 at least one hundred and ten variables in it, their periods 

 being all under eighteen hours. He could not investigate 

 the centre of the cluster, as the star images coalesced there. 

 The great separating power of the sixty-inch mirror at 

 Mount Wilson, when used as a Cassegrain, has now permitted 

 the photographic scrutiny of the central region, and Mr. 

 Shapley now announces at least twenty-three new variables 

 within a minute of arc of the centre. The brightest maxi- 

 mum of these new variables is magnitude 14-3, the faintest 

 minimum is magnitude 17-4. In some cases the range of 

 variation is half a magnitude ; in others nearly two mag- 

 nitudes. 



Mr. Shapley also discusses Cepheid variables, showing what 

 grave difficulties there are in the way of explaining these 

 by any hypothetical arrangement of pairs of stars. The 

 conclusion is that they are real pulsations in single stars of 

 ellipsoidal figure, either periodic rushes of heated gases 

 from the interior or periodic ebbs and flows of heat, causing 

 th( type of the surface to fluctuate. 



Mr. II. Shapley also writes in No. 86 of The Contributions 

 of Mount Wilson Observatory on the effei I of the darkening 

 near the limb in Algol stars. It is well known that the disc 

 of our Sun is much less luminous at the edges than in the 

 centre. The effect is probably less in Sirian than in Solar 

 stars, but it would still be sensible. In the Algol system 

 neglect of this darkening makes the bright star the smaller, 

 but taking it into account the diameters may be equal. The 

 Supposed third star which causes a perturbation with period 

 of 1-9 years is also discussed. Its light may amount to 

 one-quarter of that of the whole system, but not more than 

 this. 



MELLISH'S COMET— The orbit of this comet has been 

 deduced by Messrs. Andersen and Fischer, of Copenhagen. 



Perihelion 1915, July, 25-109 Berlin M.T. 



The comet will be visible in England till the middle of 

 May, by which time it will probably be faintly visible to 

 the naked eye. The brightness in June and July will prob- 

 ably be greater than that given above, which takes no 

 account of the physical brightening that usually takes place 

 on approach to perihelion. It is hoped that our readers 

 in the southern hemisphere will be able to obtain satis- 

 factory observations. 



The recovery ot Metcalf's Periodic Comet, recently 

 announced in " Knowledge," proved to be an error. The 

 object observed was the asteroid Lampetia. 



BOTANY. 



By Professor F. Cavers, D.Sc, F.L.S. 



INDIVIDUALITY OF THE CHROMOSOMES IN 

 PLANT NUCLEI. — A melancholy interest attaches to 

 a recently published paper by Sharp (La Cellule, Volume 

 XXIX), which represents one of the last pieces of biological 

 research done in the University of Louvain before the 

 destruction of that town by the Germans. It deals with 

 the much discussed question of the individuality of the 

 chromosomes of the nucleus, a subject which has during 

 recent years received a large amount of study at the 

 Louvain laboratory by Grdgoire and his pupils, who have 

 maintained that the chromosomes retain their individuality 

 throughout the nuclear divisions that occur in the life of 

 the organism, and are not fused together permanently 

 when the nucleus goes into the resting condition between 

 its divisions. Sharp claims that in many cases, in the cells 

 of the Broad Bean plant which he investigated, the chromo- 

 somes can be identified even in the resting nucleus, and 

 that some of the stages leading up to the splitting of the 

 chromosomes have been misinterpreted by previous investi- 

 gators, who have also overlooked important stages. Accord- 

 ing to Sharp, the actual splitting takes place at a later 



112 



