March 9, 191 1] 



NATURE 



55 



ments, it is interesting to note that its present position is 

 loh. 30-201., -13° 48-2', rouglily about one-tliird of the 

 distance from v towards K Hydrai ; it is travelling north 

 and west, towards Sextans, and its distance from the 

 earth is about 330 million miles. Prof. Barnard's observa- 

 tion, of January 8, gives a correction to_ Dr. Ebell's 

 ephemeris of +i2s., —0-5', and the ephemeris shows that 

 by April 30 the comet should be about one magnitude 

 fainter than when Prof. Barnard saw it. 



The Angular Speed of Rotation of a Long-enduring 

 Prominence.— From the study of the Kodaikanal spectro- 

 heliograms of a prominence which endured, in more or lesi; 

 the same form, for eighty-two days, Mr. Evershed arrives 

 at some important conclusions, which he publishes 111 

 No. I, vol. xxxiii., of the Astrophysical Journal. When 

 first photographed, the prominence was on the western 

 limb, was 55" high, and covered from +2° to —14° i" 

 latitude. Its seventh, and last, " limb " appearance was 

 on April 28, when it was 80" high, and extended over lati- 

 tudes — 7° to —23°; on each occasion, after the first, it 

 was seen for three successive days on the limb. Not only 

 was this object photographed on the limb, it is also seen 

 as an absorption marking on a number of " disc " photo- 

 graphs taken, and is shown as such on the four magnificent 

 photographs reproduced. 



Measures of the photographs show that the dark mass 

 of calcium (and hydrogen) vapour near the equator had, 

 during Februarv, a speed 5 per cent, greater than the 

 general surface 'of the photosphere, and, during the March 

 apparition, a speed 11 per cent, greater. They also 

 indicate that the two apparitions really represent two dis- 

 tinct masses of gas emanating from a common origin in 

 solar longitude 75°. The general aspect and behaviour of 

 the prominence suggest that it was continuously renewed 

 bv glowing gas emanating from numerous photospheric 

 orifices. 



The enormous activity attending such phenomena is 

 indicated by the fact that, on March 25, the prominence 

 extended over at least 36° of latitude, or was 250,000 miles 

 long, yet twenty-four hours later the whole object had 

 completely vanished. 



Radial-velocity measures made when the prominence was 

 on the limb, on March 17 and 18, showed that the promin- 

 ' nee, at a considerable height, was moving at a speed 

 34 per cent, greater than the normal chromosphere, and 

 they suggest that the acceleration of velocity with height, 

 discovered by Adams, may be continued beyond the limits 

 of the chromosphere. The measures were made, with a 

 radial slit set across the limb at the equator, on the Ha 

 'ine, and the difference measured was that between the 

 absorption line, representing the normal chromospheric 

 line, and the bright prominence line. 



Conjunctions of Major Planets and Stars in 1911. — ■ 

 According to Prof. Banachiewicz, in No. 4465 of the 

 Astronomische Nachrichten, there will be three near con- 

 junctions with Mars and one occupation by Jupiter this 



On May 3, at iih. (G.M.T.), Mars will be in conjunc- 

 tion with and 18" S. of B.D. -10° 5892, a star of magni^ 

 tude 7-5.; on May 10, at i2-6h., the planet will pass o-S' 

 S. of the sixth-magnitude, fundamental star h Aquarii. 

 and on August 9, at ii-7h., it will pass within 15-5" of 

 the star AG. Lpz. I. 898 (mag. 8-5) ; it is possible that the 

 unknown proper motion of the star may make this an 

 occultation. 



The star B.D. —12° 4042 (mag. 6-5) will be occulted by 

 Jupiter on August 13 at o-2h. G.M.T., and the phenomenon 

 \\-iii be observable in Australia and eastern Asia. 



AsTKoniYSics IN the United States. — The Revue 

 generalc des Sciences for February 15 (No. 3) contains a 

 very interesting illustrated article, by M. Bosler. in which 

 the author summarises the recent progress of astrophysical 

 methods in the United States. M. Bosler includes the 

 methods employed at Harvard in the systematic study of 

 the stars and their s[)(Ttrni clrt'^-^ification, the radial-velocity 

 and other researdus :it Mourn If.imilton, the multifarious 

 observations made at (ln' "Sf rkrs Observatory, and the 

 great progress in mfilKxN, in'>lruments, and knowledge 

 which has taken placf al Moiim Wilson since the solar 

 -, observalorv w.is foundi-d on its elevated sit''. The article 



is freely illustrated with photographs, and gives an excel- 

 lent idea of the great advances made in our knowledge of 

 the universe under the favourable financial and climatic 

 conditions which obtain in the States. 



Studies of Algol Variables. — The Journal of the 

 College of Science, Imperial University of Tokio, for 

 January 18, contains a paper, in English, by Mr. Naozo. 

 Ichinohe, in which the author discusses a large number of 

 variable stars of the algol type. After giving a brief 

 historical account, Mr. Ichinohe defines an algol variable, 

 and then gives a list of ninety-three stars which conform 

 to his definitions. He then discusses the periods, densi- 

 ties, distribution, magnitudes, spectra, &c., and, with a 

 number of tables, makes up a useful epitome of our know- 

 ledge concerning this type of star. 



The Spectroscopic Binary u Herculis. — In 1848, the 

 star u Herculis was suspected by Schmidt to vary ; but its 

 light-changes were puzzling, and it was not until 1869 that 

 he concluded it to be a variable, with a period of about 

 forty days, which at minimum suffered rapid changes- 

 Frost and Adams, in 1903, showed the star to be a spectro- 

 scopic binary. 



In No. 9, vol. ii., of the Publications of the Allegheny 

 observatory, Dr. Baker discusses the radial velocities of 

 [his star, determined from spectrograms taken with the 

 Mellon spectrograph, and finds it to be an eclipsing variable- 

 of the j8 LyrEE type, with a period of 2-051 days, and a, 

 secondary minimum about a day later. The presence of 

 this secondary minimum, and the presence of the fainter 

 spectrum on the plates, afford a unique opportunity of 

 ascertaining the relative densities of the two stars and' 

 other data bearing on the question of double-star evolution. 

 Dr. Baker finds "that the diameter of either star is nearly 

 six times that of the sun ; that the brighter star (visual 

 mag. = 5-0) is 7-5 as massive, but only one twenty-seventh 

 as dense as the sun, while the fainter star (mag. 6-0) is 

 2-9 times as massive and one-seventieth as dense ; that the 

 centre of gravity of the system lies well within the surface 

 of the brighter star, its mean distance from the centre of 

 each body being 2,900,000 and 7,300,000 km., respectively,, 

 and that the surface brightness of the massive star is 

 2-5 times that of the other, although the spectra are prac- 

 tically identical. If the parallax were accurately known, 

 it would be possible to determine, for this case, whether 

 helium stars, such as these two are, or solar stars, have 

 the greater surface brightness ; assuming the parallax to be 

 0-02" or greater, it would appear that the surface bright- 

 ness of the fainter star, at least, is less than that of our 

 sun. 



NO. 2158, VOL. 86] 



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