March 2, 1922] 



NA rURE 



281 



terrestrial magnetism and atmospheric electricity 

 with the Department of Terrestrial Magnetism of 

 the Carnegie Institution of Washington throughout 

 his forthcoming expedition to the Arctic regions. 

 During the North-East Passage, 1918-21, the 

 Amundsen Expedition made a series of highly valuable 

 magnetic observations at rather more than fifty 

 different points, and Capt. Amundsen's chief scientific 

 assistant, Dr. H. U. Sverdrup, has been associated 

 with the Department of Terrestrial Magnetism since 

 List October in order to complete the reduction and 

 publication of the magnetic observations thus far 

 obtained by the expedition. He will rejoin the 

 Maud, Capt. Amundsen's vessel, early in March at 

 Seattle. It is expected that Capt. Amundsen will 

 resume his Arctic expedition, the chief object of 

 which is to obtain scientific data relating to geography, 

 oceanography, meteorology, gravity, terrestrial mag- 

 netism, and atmospheric electricity, about June i. 



H.R.H. The Duke of York will open the Research 

 laboratories of the British Cotton Industries Research 

 \ssociation, Shirley Institute, Didsbury, Manchester, 

 on Tuesday, March 28. The opening ceremony will 

 take place at 3.30 p.m. 



The Societe Genevoise d'Instruments de Physique 

 informs us that it has not at the London address, 

 95 Queen Victoria Street, E.C.4, a specimen of the 

 printing chronograph referred to in Our Astronomical 

 Column on February 16, p. 217. 



The trustees of the Percy Sladen Memorial Fund 

 have given a substantial grant towards the expenses 

 of the expedition to S.W. China by Prof. J. W. and 

 Mr. C. J. Gregory, who are leaving for Rangoon at 

 the end of March. The expedition will therefore be 

 conducted as one of the Sladen Trust Expeditions. 



Professor Nils Bohr, of the University of 

 Copenhagen, will give a course of five lectures on 

 the " Quantum Theory of Radiation and the Structure 

 of the Atom " in the Cavendish Laboratory, Cam- 

 bridge, on March 6, 7, 10, 13, and 14, at 4-45 p.m. 

 The last two lectures, of a more advanced character, 

 will deal with " Selected Problems in the Theory of 

 Atomic Constitution." 



The members of the Geologists' Association of 

 London are about to entertain at dinner their retirin g 

 President, Mr. William Whitaker, F.R.S. Mr. 

 Whitaker, who is in his 86th year, joined the Geological 

 Survey in 1857 and the Geologists' Association in 

 1875. He has frequently served as a member of 

 the Council and has conducted innumerable 

 excursions. He was President from 1900 to 1902, 

 and has recently completed a second term of office. 

 The dinner will be held on Saturday, March 25, at 

 Stewart's Restaurant, 50 Old Bond Street, W., at 

 7 o'clock. A large attendance is expected. 



Ax a joint meeting of the Faraday Society and the 

 Oil and Colour Chemists' Association, to be held on 

 Thursday, March 9, at 8 p.m., in the rooms of the 

 Chemical Society, Burhngton House, W.i, a group 

 of papers will be presented dealing with the pro- 

 perties of powders considered from various aspects. 

 Prof. T. Martin Lowry and Mr. L. C. McHatton will 

 deal with the grading of powders by elutriation. 

 Prof. P. G. H. Boswell will contribute a paper on 

 elutriation from the point of view of the geologist, 

 and Dr. J. W. French will speak on grinding and 

 polishing powders. Dr. R. S. Morrell, Mr. C. A. 

 Klein, and Mr. W. J. Palmer will discuss the subject 

 from the point of view of the oil and colour chemist, 

 and Mr. R. W. Whymper will deal with certain 

 applications to cocoa and chocolate. The subject 

 will then be thrown open for general discussion. 



Our Astronomical Column. 



Relation of Spectral Type to Magnitude. — 

 The Henry Draper Catalogue of the Spectra of Stars, 

 which is now completed but not yet fully pubUshed, 

 contains as many as 225,000 stars. The classification 

 is based on the Harvard system, wherein more than 

 99 per cent, of all the stars fall into the six main 

 groups designated by the arbitrary letters B, A, F, 

 G, K, and M. It is now known, from the work of 

 Lockyer and Russell, that the actual sequences of 

 changes in a star's spectrum are from M to B as the 

 star increases in temperature (giants), and from B 

 to M as the star cools (dwarfs). Thus for each letter 

 liientioned above there are tw^o distinct kinds of stars, 

 and the nearer the letter is to M the greater this 

 distinction becomes. It is necessary, therefore, to 

 bear this fact in mind when reading the Harvard 

 'ollege Observatory Circular (No. 226) on the rela- 



ion of spectral type to magnitude by Dr. Harlow 

 -liapley and Miss Annie J. Cannon. Of the numerous 

 tables given in the paper the following abstract of 

 one of them exhibits some of the main results of the 

 investigation. 



The second column may be considered as repre- 



luting the distribution of naked-eye stars among the 

 \ arious spectral classes. It will here be seen that the 

 hot A stars exceed in number those of any other type, 

 the cooler K class running it a close second. This 



NO. 2731, VOL. 109] 



state of things is reversed in the three following 

 columns, which show a drop in magnitude for each 



Visual magnitudes brighter than 



column. In all columns, however, the A and K type 

 stars are prominent features. In discussing the 

 frequency of spectral divisions for successive fainter 

 magnitude intervals, the B type stars rapidly fall off 

 as fainter stars are considered. The A stars fall off 

 to about the 8th magnitude, but then rapidly rise 

 again. The F and M types maintain their frequency 

 nearly throughout to magnitude 8-5, but fall slightly 

 afterwards. The frequency of the G type increases 

 very rapidly throughout the whole series up to 

 magnitude 9-5, while the K class increases up to the 

 8th magnitude and then falls off. A plate accom- 

 panying the paper shows graphically many of the 

 features of the tables. 



