152 



NATURE 



[February 2, 1922 



record of topography, soil profiles, and soil types in 

 the field was a most useful section of my soil survey, 

 forming about lo per cent, of the work." As an 

 illustration of the value of the method, he showed a 

 telephotograph of an area covered by mounds of 

 fluvio-glacial sands and gravels. Mr. Monie also 

 states that the field methods he has worked out for 

 the West of Scotland can easily be applied to give 

 useful results over most areas. 



The reviewer of the translation of Prof, le Blanc's 

 "Text-book of Electrochemistry" in last week's 

 Nature, p. loi, remarked that though the title-page 

 bore the date iq2o, he could find no references later 

 than 1907. It has been pointed out to us, however, 

 that the translation, as stated on the title-page, is of 

 the fourth German edition, and that the author's 

 preface to this edition, dated 1906, is printed in the 

 volume. The translators state in their preface that 

 the work is a translation of this edition, and at the 

 back of the title-page are printed the words "Pub- 

 lished March, 1907." It was not suggested by the 

 publishers, therefore, that the work was anything 

 more than the fourth edition ; the date on the title- 

 page was merely that of the current reprint. 



Referring to the notice in Nature of January 12, 

 p. 59, of the new petrological microscope manufac- 



tured by Messrs. R. and J. Beck, the firm wishes it 

 to be known that the left-hand slow-motion milled 

 head is provided with graduations each of which repre- 

 sents o-oi of a millimetre. 



Messrs. Bowes and Bowes, Cambridge, have just 

 issued a MS. list of recent books dealing with mathe- 

 matics on sale by them, and another of works in 

 the German language. Messrs. H. K. Lewis and 

 Co., Ltd., 136 Gower Street, W.C.i, have sent to us 

 a list of the new books and new editions added to 

 their Medical and Scientific Library during October- 

 December. These lists and that of " Recent Scientific 

 and Technical Books " issued with Nature of 

 January 26 should make it possible for readers to 

 keep abreast of current scientific literature. 



Messrs. Chapman and Hall, Ltd., are about to 

 publish a book by Dr. G. W. C. Kaye entitled " Indus- 

 trial Applications of X-rays," which aims at present- 

 ing in language not too technical the various uses to 

 which the rays can be usefully applied in commercial 

 undertakings. Another book in the announcements list 

 of the same publishers is "Mechanical Testing," by 

 R. G. Batson and J. H. Hyde, 2 vols. Vol. i, which 

 will deal with the testing of materials, is expected 

 to be published in February, and vol. 2, treating of 

 the testing of apparatus, either in May or June. 



Our Astronomical Column. 



The Total Solar Eclipse of next September. — 

 The Greenwich Expedition which is being sent to 

 Christmas Island for this eclipse, consisting of Messrs. 

 H. Spencer Jones and P. J. Melotte (the former being 

 accompanied by his wife), sailed from Liverpool on 

 January 28 in the s.s. Mentor (Blue Funnel Line). It 

 is hoped by May to have the instruments ready for 

 observation ; the apparatus taken weighed 4 tons, 

 including the 13-in. astrographic equatorial, which 

 will be used for stellar photometry, to connect the 

 magnitude scales of the northern and southern hemi- 

 spheres, in addition to the eclipse programme, which 

 is simply a repetition of the testing of the Einstein 

 light-shift. The stars are fainter than those of the 

 1919 eclipse, but the replacement of the coelostat by 

 an equatorial should bring a great gain in definition. 



The Times of January 27 makes the welcome an- 

 nouncement that the Commonwealth Government will 

 put a warship at the disposal of the parties visiting 

 Wollal, Western Australia ; these include a large 

 party from the Lick Observatory, also parties from 

 Toronto and New^ Zealand and some Australian astro- 

 nomers. This will be of great assistance to the parties, 

 but will not remove all their difficulties, as there 

 is no harbour in the neighbourhood, and ships have 

 to anchor some miles out, and land passengers and 

 goods by boats through a surf that is often heavy. 



Mr. J. Evershed, director of Kodaikanal Observa- 

 torv, hopes to observe the eclipse from the Maldive 

 Islands. 



The Pleiades. — Lick Obs. Bull. No. 3-^3 contains 

 an important study of this cluster bv Mr. Robert 

 Trumpler. The stars belonging to it are distin- 

 guished from the background stars by their proper 

 motion ; Boss's value for the bright stars is 5-4" per 

 century in position angle 157-9°. A list is given of 

 246 stars, of magnitudes between 28 and 15-2, that 



NO. 2727, VOL. 109] 



are concluded to be members of the cluster ; this con- 

 clusion is supported in the case of the fainter stars 

 by the fact that the average motion of stars of these 

 magnitudes is much smaller. The conclusion is 

 strengthened by an examination of spectral types ; 

 these are found directly for the stars brighter than 

 magnitude 11, and inferred from the colour-index for 

 the fainter ones. On plotting spectral class against 

 magnitude a smooth curve is found, which descends 

 less steeply in the middle portion than at the ends ; 

 it is interesting to note that a practically identical 

 curve was reached at Greenwich by Messrs. Davidson 

 and Martin on plotting effective wave-length against 

 spectral type for stars in the Greenwich astrographic 

 zone. 



Inferring the absolute magnitudes for each spectral 

 type from stars of known parallax, the parallax 

 o-oo8" is found for the Pleiades. The hypothetical 

 parallax deduced from the binaries in the cluster is 

 o-oio", while Hertzsprung and Hartmann found 

 0014" from the parallactic motion of the group. It 

 is inferred that the round value of 100 parsecs, or 

 320 light-years, is close to the true distance. One very 

 interesting fact is that the red and yellow stars in 

 the cluster are dwarfs, the only giants being those of 

 type B and perhaps a few of type A. It will be 

 remembered that on Russell's theory the B type is 

 the latest of the giant stages, so that the cluster 

 would seem to be in its old age. Examination of 

 the binary stars supports Aitken's conclusion that 

 stars of considerable mass are more likely to 

 divide. Another point noted is the deficiency of stars 

 of tvpe F, suggesting that this may be a short-lived 

 stage. The average star density of the whole group is 

 about ten times that in the sun's neighbourhood. 

 That in the centre of the group is still greater. Cor- 

 fecting for the sun's motion, the speed of the group 

 is 9 km. /sec. 



