114 



NATURE 



[April ii, 191 8 



OVR ASTRONOMICAL COLUMN. 



Spectrum and Radial Velocity of N.G.C. 1068. — 

 Further photographic observations of the spectrum of 

 the spiral nebula N.G.C. 1068 (M77) have been made 

 at Flagstaff by Dr. V. M. Slipher (Lowell Observatory 

 Bulletin, No. 80). Among the photographs obtained 

 was one taken with a two-priSm spectrograph, which 

 received a total exposure of thirty-five hours during 

 five nights. Besides confirming the composite char- 

 acter of the spectrum and the high velocity previously 

 recorded, this photograph shows that the bright 

 hydrogen lines extend farther into the fainter parts of 

 the nebula than do the two green nebular lines, and 

 that both bright and dark lines are strongly inclined. 

 The inclination is about 5°, and indicates a rotation 

 about an axis through the shorter diameter of the 

 nebula, the velocity of rotation being approximately 

 300 km. per sec. at i' from the nucleus. This is the 

 highest rotational speed which has yet been recorded, 

 and there is evidence that the inner part is turning 

 into the arms of the spiral, like a winding spring, as 

 in the case of other spirals in which rotation has been 

 observed. A peculiar feature of the emission lines is 

 that instead of appearing as simple images of the slit, 

 they appear as small discs ; pressure increasing to- 

 wards the nucleus is a possible explanation. The re- 

 cent photographs consistently indicate the enormous 

 receding velocity of 1120 km. per sec. for this nebula. 



Changes in the Spectrum of 7 Argus. — A pre- 

 liminary account of some photographs of the spectrum 

 of 7 Argus, which were taken at Cordoba with a 5-in. 

 objective prism attached to the astrographic equatorial, 

 has been given by Dr. C. D. Perrine {Astrophysical 

 Journal, vol. xlvii., p. 52). The star is well known 

 as being the brightest example of the Wolf-Rayet type, 

 and the new observations appear to show compara- 

 tively rapid fluctuations in the structure of H,3, which 

 is doubly reversed. While the bright band was most 

 intense on the red side of the weak absorption line 

 on plates taken in August, 1917, it was brightest on 

 the violet border during November. Variations in the 

 widths of the bright bands in the region A 450 are also 

 indicated. From a comparison with earlier records 

 by other observers, it is concluded that considerable 

 changes have occurred during the last twenty years. 

 Dr. Perrine has further noted a broad, faint brighten- 

 ing in the region of the chief nebular line, and a sus- 

 pected brightening in the region of the second nebular 

 'line ; it may be suggested, however, that these ar^ not 

 the nebular lines at all, but the adjacent lines of 

 helium, as previously photographed at Johannesburg 

 by W. M. Worssell. The latter photographs, it may 

 be recalled, gave no certain evidence of secular changes 

 in the spectrum. 



United States Naval Observatory. — ^The report of 

 the U.S. Naval Observatory for the year ending June 

 30, 1917, has been received. The routine observations 

 were continued without intermission, including meri- 

 dian work, observations of comets and occupations 

 with the equatorials, observations of asteroids of 

 special interest, and photographic investigations of the 

 'variation of latitude. The nautical instrument repair 

 shop was especially active, and has continued to prove 

 economical both in time and expense; more than 

 3000 instruments were put in order during the year. 

 The observatory has continued to encourage sugges- 

 tions and developments of methods and instruments 

 for rlavigation, particularly for submarines and air- 

 craft. 



Corrections to the Bonn Durchmusterung. — 

 Prof. F. Kiistner, director of the Bonn Observatory, 

 publishes in Astronomische Nachrichten, 4929, a use- 

 ful list of corrections' to the B.D., which all astro- 

 NO. 2528, VOL. lOl] 



nomers who use that work would do well to incor- 

 porate in their copies ; some of the corrections refer to 

 the star-positions, others to their magnitudes, others 

 to the catalogue references, whilst a list is given of 

 the stars in each volume that have been recognised as 

 variables since the publication of the B.D. Consider- 

 ing the immense number of stars in the catalogue, and 

 the small size of the instrument with which it was 

 made, the list of errata is extremely short, and reflects 

 the greatest credit on Argelander and his assistants. 



AURORAL OBSERVATIONS IN THE 

 ANTARCTIC. 

 nPHE paper referred to below ^ was prepared, the 

 -•- author tells us, in 191 1, but printing was delayed 

 as Sir E. Shackleton, the leader of the 1908 Antarctic 

 Expedition, hoped to publish the scientific work as a 

 complete series. That idea unfortunately had ulti- 

 mately to be abandoned. The paper is a very valu- 

 able contribution to our knowledge of aurora, and its 

 appearance, if late, is very welcome. HThe auroral log 

 occupies pp. 155-200, and includes particulars of the 

 times when aurora was observed, and various descrip- 

 tive information as to the nature and trend of the 



Fig. 1. — Daily time-distribution at Cape Royds. Graph- 

 ical illustration of the relative frequency of auroral 

 phenomena at different hours of the day. Radius 

 vectors on scale such that 3/i6oth in. equals one hour's 

 display. 



aurora when it consisted of curtains, arcs, or streamers 

 having a definite direction. A preface explains the 

 scheme of observations, and the terms employed are 

 dealt with in the introductory remarks. Sir Douglas 

 considers the curtain the fundamental type of aurora. 

 When streamers alone are visible, they represent in 

 general, he thinks, "the visible parts of an invisible 

 curtain." 



A discussion of the phenomena is given in a sum- 

 mary, pp. 201-12. This is illustrated by a plate and 

 by Figs. I and 2, here reproduced. Fig. i shows the 

 diurnal variation in the frequency, and Fig. 2 the rela- 

 tive frequency with which aurora was observed in the 

 different geographical directions. Only the observa- 

 tions of June, July, and August, 1908, were employed. 

 The station being at 77° 32' S. lat., the sun was con- 

 tinuously below the horizon during these months, 

 so the disturbing effects of daylight or twilight were 

 at a minimum. Observers in the northern hemisphere 

 have usually, if not always, found the maximum fre- 

 quency before midnight. At Cape Royds, as Fig. i 

 shows, it appears near 3. a.m. This is in general 

 agreement with the conclusions reached by Mr. L. C. 



1 "Auroral Observations at the Cap' Royds Station, Antarctira. British 

 Antarctic Expedition, igoS." By Sir Douglas Mawson. (From Trans. Roy. 

 Soc. of S. Australia, vol. xl., igi6, pp. 151-212.) 



