February 25, 1909] 



NA TURE 



499 



ing scvintc'on results show ;i mean difference of 4.S5 lb. 

 per square inch in the maximum shearing stress at breali- 

 down, giving a discrepancy of 3 per cent. only. By 

 calculation from the results of these tests, it is shown that 

 the maximum tension hypothesis is wrong by 50 per cent., 

 and the stretch hypothesis by 35 per cent., taking Poisson's 

 ratio as 0-3. Mr. Turner's experiments may therefore be 

 regarded as giving strong support to Guest's theory. The 

 author proposes to investigate stress of three dimensions, 

 and also to find how far the results obtained for static 

 stress may be applied to the case of stress the magnitude 

 of which is subject to constant variation. 



The twentieth annual issue — that for igog — of the 

 ■■ Public Schools Year-book and Preparatory Schools Year- 

 book " is now available. Among new features character- 

 ising the present volume may be mentioned articles on the 

 universities, giving full details of universities other than 

 Oxford and Cambridge ; additional information on qualify- 

 ing for the Scots Bar and the profession of Writer to 

 the .Signet; an article dealing with chemistry as a pro- 

 fession ; and a list of lecturers who attend public and 

 preparatory schools. To parents and others selecting 

 either a school or a profession for their boys this enter- 

 prising annual should prove invaluable; it is published by 

 Messrs. .Swan Sonncnschcin and Co., Ltd., and its price 

 is 5S. bd. net. 



OfR .\SlRO)<OMlCAL COLUMN. 



-■VSTRONOMICAI. OCCURRENCES IN M.ARCK : — 

 March I. lih. 32m. Nf p'line in coniunclion with the Moon 

 (Nep una 2° 37' S.). 



4. I2h. .i7ni. Variable star A'gol at minimum. 



5. 2ih. 50m. lupi'er in conjunction with the Mjon 



(Japiter 3' 42' S.) 

 7. 9h. 26m. Variable star A'enl at minimum. 

 16. 3h. ^m. Mars in conjinciion with the Moon (Mars 



i°26'N.). 

 ,, I4h. 19m. Uranus in conjunction with ihe Moon 



(Uianus 2° 4' N.). 



20. I3h. on). Venu< in conjunction with the Mcnn 



(Venus 3° 52' N.). 



21. 23h. 46m. Saturn in conjunction with the Moon 



(Saturn 2" 41' N. ). 



26. Sh. 54"". Mais and Uranui in conjunction (.Mais 



0° iS'S.). 



27. Ilh. bm. Algol at minimum. 



28. I7h. 30ni. Neptune in conjunction with the Moon 



(N. p une 2" 51' S.). 

 30. '. 8h. 4Cin. Red spot central on disc of Jupiter. 



.\ Bkilli.axt Meteor .\nd its Tr.ain. — A brilliant meteor 

 w^as seen over a large part of the south of England about 

 7.30 on Moi.day evening, February 22. A luminous cloud 

 or streak was visible for a long time after the meteor 

 itself had disappeared. The Rev. F. J. Jervis-Smith, 

 F.R.S., writing from Battramsley House, near Lyming- 

 ton (long. 1° 32' \V., lat. 50° 48' N.), says : — " At 7.30 p.m. 

 on February 22 my attention was directed by my gardener 

 to a luminous streak or band left by a meteor, which he 

 had seen about twenty minutes before while cycling near 

 Brockenhurst. The streak was not straight, but slightly 

 curved, first towards the north, then to the south, then 

 again to the north, then, turning through about 110° to 

 its mean path, towards the south, it was lost to sight. 

 The streak passed through £ Ursae Majoris and y Cassio- 

 peia;. The streak was clearly visible up to 8 p.m. The 

 width of the luminous band covered, roughly, one-eightli 

 of the distance between 5 and f Vrsx Majoris. The 

 gardener described the luminous head of the meteor as 

 being like the head and shoulders of a whale in shape. 

 While I watched the streak a small meteor crossed the 

 heavens, starting near Polaris, the path being south to 

 north." 



Miss Annie L. Waud, observing at Farnham, first 



KO. 2052, VOL. 79] 



observed the luminous appearance at 7.50 p.m. " It was 

 then in Eridanus, and was a glowing streak of light, with 

 two short branches or tails ; the streak rapidly moved 

 towards the north-west, the tails growing longer, the 

 upper one gradually spreading through Orion, first through 

 Rigel and then through the belt, finally stretching far 

 beyond and above that constellation. The mass grew 

 fainter as it sank at 8.30 p.m. towards the west,, but .the 

 upper tail, which was now forked, was distinct until 

 9.30 p.m." 



Dr. T. K. Rose saw this luminous train between Orion 

 and the horizon, at Northwood, " from about 7.45 to 

 betw'een 9 and 10 o'clock, when it was lost in mist near 

 the horizon. It was faint, and could not have been seen 

 but for the brilliance of the night." The apparent shape 

 of the luminous mass changed greatly during this interval, 

 but no nucleus was seen by Dr. Rose at any time. With 

 an opera-glass stars could lie seen through the cloud. 



Qu.ANTiT.*TivE Measures of the W.^ter-v.'vpour in the 

 Martian Atmosphere. — From measures of the relative 

 intensities of the a, water-vapour, band in the spectra of 

 Mars and the moon recently obtained by Mr. Sliphcr at the 

 Lowell Observatory, Prof. Very has derived quantitative 

 results showing the probable ratio between the amount of 

 water-vapour in the Martian atmosphere and the amount 

 of water-vapour in the Flagstaff atmosphere at the time 

 the spectrograms were taken. 



The measurements were made with a " spectral-band 

 comparator " devised by Prof. Very, the narrower com- 

 ponent of the a band, X 7160—7200, being measured in 

 overv case ; the relative intensity of the C band was also 

 measured, on each set of spectra, as a check. 



The readings given by the comparator w'ere found to be 

 very consistent, but were merely conventional. Reducing 

 these measures so that they represent absolute intensities. 

 Prof. Very finds that the a band in the spectrum of Mars 

 is about 45 times as strong as in the lunar spectrum, and 

 a further reduction brings out the fact that at . the time 

 of exposure the Martian atmosphere must have held in 

 suspension about 1-75 times as much water-vapour as 

 existed in the earth's atmosphere above Flagstaff. 



Finallv, Prof. \'ery arrives at the conclusion that whilst 

 the atmosphere above Flagstaff contained sufficient pre- 

 cipitable water to give an average layer of about 8 mm. 

 in depth, the average layer of precipitable water on Mars 

 was about 14 mm. ; the mean value for the earth would 

 probablv be three or four times as great (Lowell Observa- 

 tory Bulletin, No. 36). 



.\bsorption of Light in Space. — In a paper appearing 

 in No. I, vol. xxix., of the Astrophysical Journal (p. 46, 

 January), Prof. Kapteyn discusses one or two phenomena 

 which point to the absorption of star-light during its passage 

 through interstellar space. 



That the stars appear gradually to thin out as we recede 

 farther and farther from the solar system is a priori 

 evidence that some such absorption exists, otherwise we 

 must assign to the sun a unique position in the universe, 

 that is, the place of maximum density. 



In a previous discussion Prof. Kapteyn found a pro- 

 visional value for the absorption amounting to 0-016 of a 

 magnitude for the distance of thirty-three light-years, as 

 an average for the whole of the sky. Recently obtained 

 results of spectral classification, from Harvard, permitted 

 him to make another attack on the problem by investigating 

 the probable average distances of Miss Maury's two classes 

 of stars of which a Bootis and o Cassiopeiae are typical. 

 The spectra of the former of these two classes exhibit less 

 general absorption than do those of the latter, and from 

 an analysis of the proper motions given in Newcomb's 

 " Fundamental Catalogue " Prof. Kapteyn finds that, as a 

 rule, the proper motions in the a Bootis division greatly 

 exceed those in the a Cassiopeiae division. This is evidence 

 that thev are. as a class, nearer to us, and would, there- 

 fore, exhibit less general absorption, if it were due to an 

 absorbing medium, than would the a Cassiopei.ne stars. 

 Thus the present investigation strengthens the probability 

 of the existence of such an ab.sorbing medium. 



The Orbit of 9 Aqvilje. — From radial-velocity observa- 

 tions made at the .'\llegheny Observatory during 1907, Mr. 



