136 



NA TURE 



[June i i, 1908 



OVR ASTRONOMICAL COLUMN. 



Bright Meteor. — Mr. Denning at Bristol saw a bright 

 meteor of about first magnitude at iih. 12m. on June 2 

 with path from 301°+ 50° to 265° + 55°, and directed from 

 the shower of Pegasids at 334° + 28°, to which he recently 

 directed attention in Nature. The meteor left a streak of 

 about 10° amongst the stars of Cygnus and Draco. At 

 Bristol the midnight sky of June 2 was magnificent, the 

 stars being unusually bright and the firmament remarkably 

 dark, and comparable with some of the evenings of early 

 autumn. 



The Total Solar EclIpse of May S, 19 10. — In a letter 

 to the Observatory, Mr. J. F. Tennant points out the 

 availability of Tasmania as an observing station for the 

 eclipse of the sun due to talce place on May 8, 1910. The 

 duration of the total phase will be something like three 

 minutes, but the sun will, at most places, apparently be 

 at a low. altitude ; in fact, except at the extreme N.W., 

 the sun sets partially eclipsed. Particulars as to times 

 are given in the letter, and the writer states his intention 

 to obtain particulars concerning the climatic probabilities, 

 &c. (the Observatory, No. 397, p. 250, June). 



The Dark D3 Line in the Sun. — In the June number 

 of the Observatory (p. 250) Mr. Buss returns to the dis- 

 cussion anent the presence of the helium absorption line 

 in the solar spectrum. Among other things, he points out 

 that, according to Mr. Evershed's recent letter, the posi- 

 tion of the darlc D, line is now given as being on the red 

 side of the bright chromospheric line, whereas it was 

 previously stated to be on the more refrangible side. 



Mr. Buss adds that of 358 observing days in 1906 and 

 1907 he made spectroscopic observations on 317 days, and 

 was able to detect the Dj absorption on 236 days, or on 

 about 75 per cent, of the total number. This indicates 

 that the phenomenon of helium absorption over active 

 solar areas is not so rare as has been thought, and Mr. 

 Buss suggests that, with a more refined equipment than 

 his, a practical permanency of the phenomenon over such 

 areas, with or without spots, might be established. 



It is interesting to note with regard to this that at the 

 meeting of the British Astronomical Association held on 

 April 29, Father Cortie expressed the opinion that for this 

 class of work a telescope of not very large aperture and 

 a spectroscope of moderate dispersion were required. 



Position of the Axis of Mars. — In No. 4251 of the 

 Astronor>iische Nachrichten (p. 39, May 29) Prof. Lowell 

 gives the results obtained from his measures of the posi- 

 tion of the axis of Mars during 1907. Between September 

 23 and December 16, igo", 198 determinations of the 

 position-angle of the south polar cap were made by Prof. 

 Lowell and seventy-nine by Mr. Lampland. The measures 

 were made in three different ways : — (i) with the micro- 

 meter thread cutting off equal segments below the cap ; 



(2) with the thread tangent externally to the cap ; and 



(3) with the thread tangent internally to the cap, and on 

 collating the results it was seen that each method is 

 subject to systematic errors. To throw some liglit on the 

 question of these errors, an artificial planet was devised 

 by Mr. Lampland on which measures were made by both 

 observers, under conditions as far as possible identical with 

 the true conditions. The results of these observations 

 showed that the dichotomy measures are more trustworthy 

 than the tangential, that they are decreased by phase, and 

 that the tangency measures are too large. 



Combining the results for the measures made during 

 1901-7, Prof. Lowell obtains as the general mean for the 

 position of the axis R..'\. = 3i5° 38', dec. = 54° 39', and for 

 the obliquity of the Martian ecliptic 23° 8'. He then gives 

 a table comparing his results with others obtained since 

 1781, and points out that there is apparently a steady 

 decrease in the obliquity if Cerulli's observations of 1896-7 

 be excepted ; of this phenomenon he offers no explanation. 



The Orbit of a Andromeda. — From spectrograms taken 

 at the Potsdam Observatory during the period 1901-7, Herr 

 Ludendorff determined an orbit for the spectroscopic 

 ■binary a .•\ndromedre, and now publishes his discussion in 

 No. 4250 of the Aslroiiomisclie Nachrichten (p. 23, 

 May 21). For the period he finds 967 days, a value which 



NO. 2015, VOL. 78] 



he considers certain to within 01 day. In the discussion 

 he confirms Sir Norman Lockyer's remarks as to changes 

 in the spectrum, and records that he has on several plates 

 observed the Mg line at X 4481 doubled. 



The Eccentricities of Comet Orbits. — In No. 113, 

 vol. .xix. (pp. ti7-7i), of the Publications of the Astro- 

 nomical Society of the Pacific, which we have just re- 

 ceived, there is an interesting address by Prof. Leuschner 

 on the probable general form of comet orbits. Prof. 

 Leuschner raises strong objections against the prejudice 

 which assumes all cometary orbits to be parabolic unless 

 it can be proved very certainly that they are elliptic or 

 hyperbolic. In support of his suggestion that the para- 

 bola may be the exception, and not the rule, he gives two 

 tables, the first of which shows the percentage of parabolic 

 orbits of comets appearing in three different periods. For 

 the last period (1846-95) only 54 per cent, of the deter- 

 mined orbits had the eccentricity i-o, and therefore it 

 seems no more probable that a comet's path should be 

 parabolic than that it should not. The second table 

 classifies the orbits according to the duration of visibility 

 of the comets, and here it appears that the longer the 

 comet is observed the more probable it becomes that the 

 orbit cannot be satisfied by a parabola. Of comets 

 observed for more than 240 days, it is doubtful whether 

 any had parabolic orbits. 



THE KOYAL OBSERVATORY, GREENWICH. 

 T^HE annual visitation by the Board of Visitors of the 

 Royal Observatory, Greenwich, was held on Wednes- 

 day, June 3', when the customary report was presented by 

 the Astronomer Royal dealing with the work carried out 

 during the twelve months ending 1908 May 10. A 

 summary of the chief points of the report is given below. 



Among other matters, it is interesting to note that 

 various national undertakings of importance were, or 

 are being, facilitated by the loan of instruments by the 

 observatory authorities. Thus the observers attached to 

 the British .'\ntarctic Expedition (1907) are using the 4-inch 

 Simms' telescope No. 2, Captain Monro, R.N., used the 

 transit instrument D in the determination of the longitude 

 of Ascension, whilst a very interesting collection of 

 historical and modern astronomical and meteorological 

 instruments, models, photographs, &c., illustrating the past 

 and present work of the observatory, is being exhibited 

 in the Science Section of the Franco-British Exhibition. 



Referring to the work done with the transit circle, the 

 report slates that the system of inclined wires formerly 

 used has been replaced by a system of two close vertical 

 wires and one horizontal wire, and the method employed 

 for illuminating the field has beefl changed to that applied 

 so successfully to the altazimuth last year. A series of 

 observations is now being carried out in order to compare 

 the results obtained under the respective conditions of 

 illumination, and it is hoped that a discussion of the results 

 may throw some light on the question of the magnitude 

 equation in the observation of the fainter stars. 



The transit was employed for the usual observations of 

 the sun, moon, planets, and fundamental stars, the work- 

 ing list being made up by the inclusion of stars of the 

 ninth magnitude and brighter between the parallels of 

 north declination -1-24° to -1-32°, which will serve as refer- 

 ence stars for the Oxford astrographic zones. Eight 

 thousand seven hundred and twenty-three transits and 7960 

 circle observations were tal<en during the year. 



From the observations made in 1905, applying Bessel's 

 refractions, 38° 31' 2i"-'ja was determined as the co-latitude, 

 whilst those made in 1906, with Pulkowa refractions, gave 

 the value 38° 31' 2i"-67. The reduced solar observations 

 of 1906 show the correction to the tabular values for the 

 obliquity of the ecliptic to be — o"-o9, and the observations 

 of the summer and winter solstices indicate that the mean 

 of the observed distances from the pole to the ecliptic is 

 apparently o".oo5 too great. 



Each day, when practicable, three or more observations 

 of level and nadir were made, and it was found that the 

 diurnal changes of level ranged from +o".i3 at noon, to 

 o".oo at 6 p.m., to -|-o"-i8 at midnight; the corresponding 

 values for the nadir were found to be -l-o".i7, o".oo, and 



