426 



NATURE 



[May 25, 1911 



OVR ASTRONOMICAL COLUMN. 



Astronomical Occurrences for June:— 

 June 1. 5h. cm. Mercury at greatest elongation W. of the 

 Sun (24' 30' W.). 



6. I5h. cm. Mars at greatest heliocentric latitude S, 



7. I7h. 6m. Jupiter in conjunction with the Muon. 



(Jupiter 1° o' N.)- 

 14. I4h. !6m. Uranus in conjunction with the Moon. 



(Uranus 4* 35' N.). 

 20. I2h. 44nn. Mars in conjunction with the Moon. 



(Mars o* 12' N.). 

 22. ih. 35m. Sun enters Sign of Cancer. Solstice. 

 22. 22h. 38m. Saturn in conjunction with the Moon. 



(Saturn 3' 3' S. ). 

 25. 9h. 14m. Mercury in conjunction with the Moon. 



(Mercury 3° 32' S.). 

 27. 2h. 3Sm. Neptune in conjunction with the Moon. 



(Neptune 5° 28' S.). 

 29. 5h. 8m. Venus in conjunction with the Moon. 



(Venus 3" 40' S.). 

 29. I3h. cm. Mercury in perihelion. 



The Tail of Halley's Comet on May 20, 1910. — No. 

 4406 of the Astronomischc Nachrichten contains further 

 notes on the question of the direction of the tail of 

 Halley's comet on the evening of May 20, 1910. Piof. 

 Eginitis returns to the discussion, with M. Antoniadi, con- 

 cerning the appearance of a tail directed towards the sun, 

 and suggests that the latter has failed to recognise the 

 e.\ceptional position of the tail, with regard to the earth 

 and sun, at the time, and also its curvature ; such con- 

 ditions would account for the phenomena observed at 

 Athens about which Prof. Eginitis has no doubt and M. 

 .Antoniadi contends were impossible. 



The Spectrum of the Ring Nebula in Lyra. — Some 

 interesting spectra of the Ring Nebula are published by 

 Mr. Kelvin Burns in No. 193 of the Lick Observatory 

 Bulletins. The photographs were taken with a slitless 

 spectroscope attached to the Crossley reflector, in order to 

 determine the spectral type of the central star. Stained 

 and unstained plates were employed, and, in passing, it is 

 interesting to note that a " Cramer Crown " plate stained 

 twenty-one days previously was 50 per cent, faster in the 

 red than a newly stained plate from the same box. The 

 length of the spectrum is only 33 mm. between X\ 6560 

 and 3730, and the width of the image of the Ring is 

 1-6 mm. in declination. 



A comparison of adjacent stellar spectra with the spec- 

 trum of the central star showed that while between 

 A\ 6600 and 5800, the latter was only as bright as a 

 14-2 mag. star of type A or F ; at A 3300 it was as bright 

 as an F-type star of magnitude 12-4. In fact, the spec- 

 trum of the central star is relatively stronger in the ultra- 

 violet than that of the bluest of the many Orion-type 

 stars which have been photographed with the same instru- 

 ment ; yet there is not the great difference between the 

 visual and photographic magnitudes of this star that there 

 is generally thought to be. Mr. Burns states that, if 

 isolated, both the central star and the other star within the 

 Ring would be easy objects for moderately laige tele- 

 scopes ; he finds their visual magnitudes, by photographic 

 methods, to be 14-1 and 14-7, while their photographic 

 magnitudes are 13-2 and 14-5 respectively. The similarity 

 of the spectrum of the central star to the spectra of 

 central stars, or condensations, in other nebulae removes 

 any doubt as to its connection with the nebula. 



The following radiations were found in the spectrum of 

 the nebula itself : — \X 3450, 3730, 3870, 3970 (He), 4100 

 (H8), 4340 (Hy), 4600, 4860 (H3), 4060-5010 (chief nebula 

 line), 5880 (D,), and 6560 (Ho). Of these, the radiation 

 at A 3730 is by far the strongest, on the ordinary plate, 

 and is followed by the chief nebula line ; the hydrogen 

 lines are relatively faint. The sizes of the rings due to 

 X 3730 and the hydrogen lines appear to be the same, 

 while those due to the nebula lines XX 3870 and 500 appear 

 to be smaller. The monochromatic images of the ring 

 show far more detail than a composite image, a fact which 

 suggests that they differ in detail. 



Proper Motions of St.4Rs between +75° and +80° 

 Declination. — By the comparison of the positions deter- 



NO. 2169, VOL. 86] 



mined at the Katan Observatory with thote g! 

 tw<.nty-two earlier catalogue*, I'rof. Dubiago hav 

 mined the proper motions of some 730 stars, and • 

 them in No. 4496 of th«> Astronomische Nadi 

 these stars occur in the Kasan A.G. zone bctv. 

 tions +75° and +80°, and the complete rekultk arr ■■■> 

 appear in No. xv. of the Publications of the Ka^.' 

 Observatory. 



The Gyro-compass. — A brief description of ti. 

 compass, which was exhibited at a recent meeting o) • 

 Royal Astronomical S<K:iety, appears in the May numh- r 

 of The Observatory (No. 435, p. 190). This compasii i> 

 quite independent of the earth's magnetism, and m.i, 

 therefore be employed in many positions where ;im 

 ordinary magnetic compass would be useless. It wai>. :-. 

 fact, primarily designed for use in polar research, but n<.v. 

 proves to be (juite unsuitable ; it is, however, trustwort!.;. 

 between latitudes 70" N. and S., and is being adopted h, 

 several Governments for use in their navies. 



The rotating disc is floated on mercury, so that it i- 

 free to move in two directions, and the rotation of th" 

 earth causes the axis to set itself due north and south. 

 The axis is geared up to an indicator, so that the ner-dl^ 

 always points N. and S. when the gyro is running. Th- 

 rotation of the disc is produced by an ingenious elecfr;< 

 motor of which the disc forms part, and the inherf^rt 

 tendency to prolonged oscillation is overcome by a mo'^t 

 ingenious system of damping by currents of air, the appli- 

 cation of the blasts depending upon the amplitude of th^ 

 oscillation at the moment. 



A fuller description of the instrument is given by Mr. 

 G. K. B. Elphinstone in a book, " The Anschiitz Gyro- 

 compass," published by Hugh Rees, Ltd. 



Ancient Observatories in India. — An illustrated d' - 

 scription of the five astronomical observatories erected at 

 the beginning of the eighteenth century by Saway Jay 

 Singh, the Maharaja of .'\mbhery in Rajputana, is one 

 of the interesting papers in the May number of ^ 

 L'Astronomie. M. Ducret, who describes the equipments, * 

 states that the observatories were situated at Benares, * 

 Muttra, Delhi, Ujjain, and Jaipur, but with the excep- 

 tion of the last named they are in a sad state of ruin. A 

 photograph of the Jaipur Observatory shows huge masonry - 

 erections by which the altitudes and azimuths of the j 

 celestial bodies could be determined. The installation , 

 shows that in 1718-34, when the observatory was erected, i 

 the study of astronomy of position was well advanced in I 

 India. | 



THE BRITISH SOLAR ECLIPSE 

 EXPEDITION. 



March 30, 191 1. 

 AT the moment of writing we are fifty-five da>s out 

 •^^ from home, and are steaming along steadily in 

 H.M.S. Encounter towards the island of Vavau, which 

 we hope to reach on Sunday evening ne.xt (April 2). Sine- 

 leaving Sydney, on March 25, we have experienced a 

 N.E. or head wind all the time, which has somewhat: 

 reduced our speed. To-day we are in lat. 25° 205' and 

 long. 174° E., i.e. we are well to the north-east of Norfolk 

 Island and to the south of Hunter or Fearn Island. 



When boarding the ss. Otway at Tilbury on February 3, 

 I was the sole representative of the Solar Physics Observa- 

 tory's expedition on board, for Father Cortie and Brother 

 McKeon, who joined the ship at the same time, represent 

 the party sent out by the Joint Eclipse Committee. It 

 was not long before I discovered that many cases con- 

 taining self-recording instruments, books, photographic 

 materials, lantern-slides, &c., for use on the voyage, were 

 not placed in my cabin, and it was only at Port Said that 

 I finally heard by cable that they were all neatly stowed 

 away in No. 2 hatch with hundreds of tons of cargo above 

 them, and therefore inaccessible until Sydney was 

 reached. Fortunately, I had my 5x4 Kodak with me, 

 and supplies of films were easily obtained at Marseilles, 

 Naples and Colombo en route. i 



On the whole, the weather was cold for the time i)S\ 

 year on the way out to .Australia, and it was only in the 

 doldrums that a high temperature and moisture-laden 



