June 8, 19 16] 



NATURE 



1 1 



OVR ASTRONOMICAL COLUMN. 



A Large Group of Sun-spots. — A remarkable spot 

 outburst, including a great irregular active spot fol- 

 lowed by a widespread disturbed area, was easily seen 

 with the help merely of dark glasses on May 27, 28, 

 and 29. Its reappearance on the eastern limb should 

 occur about June 12 or 13. 



The Total Solar Eclipse of February 3, 19 16. — 

 A brief announcement in the Publications of the Astro- 

 nomical Society of the Pacific (April) states that 

 totality was observed through thin clouds by a party 

 from the Argentine National Observatory stationed 

 at ■ Tucacas, Venezuela. Astronomer Chaudet had 

 charge of the expedition, and the equipment included 

 two cameras for coronal photography, two prismatic 

 cameras for recording the "flash" and corona spectra, 

 a small slit spectrograph, and a photometer. 



I The Spectrum of Nova Gemixorum No. 2.— On 

 • a photograph taken by Messrs. Adams and Pease at 

 Mount Wilson on the nights of February 12 and 13, 

 with a total exposure of nine hours, the spectrum still 

 shows Wolf-Rayet features — bright hydrogen lines and 

 a very prominent bright band at A 4686 are mentioned. 

 The continuous spectrum is described as very strong 

 (Publications, Astronomical Societv of the Pacific, 

 No. 163). 



Latitude Observations by Photography. — The work 

 of the International Latitude Commission bids fair to 

 be remembered as the last great piece of visual 

 measurement. The results obtained at Gaithersburg 

 alone would demonstrate that by means of photo- 

 graphy here, as in so many other departments of 

 astronomy, a precision of superior order is now obtain- 

 able. From this point of view the report by Dr. Ross 

 might almost be regarded as epoch-making (Special 

 Publication No. 27, U.S. Coast and Geodetic Survey, 

 a quarto memoir of 127 pages and 18 plates). The 

 photographic zenith tube as developed by Dr. Ross is 

 a remarkable and ingenious instrumental achieve- 

 ment, and the detailed description will no doubt be 

 read with the greatest interest by instrument-makers 

 in this country. It consists essentially of a fixed 

 vertical tube carrying a horizontal lens over a dish of 

 mercury, forming an image of zenith stars just below 

 the plane lower surface of the lens on a photographic 

 plate. The objective end can be rotated carrying with 

 it the plate-holder, during exposures by clockwork 

 through a magnetic clutch at suitable rate to give 

 point irnages, or by hand for reversal through 180°. 

 The design of the lens practically eliminates the effect 

 of errors of level. Freedom from tremor in the mer- 

 cury reflector was secured by floating the amalgamated 

 dish in a second placed on a tripod resting on a 

 small pier independent of the main concrete base of 

 the tube. The visual routine programme was con- 

 tinued without intermission, and thus a valuable com- 

 parison of the two methods has been secured. 

 Numerically the superiority of the photographic pro- 

 cedure is most obvious when the results from a single 

 pair of stars are considered, the mean accidental error 

 of a determination of latitude being reduced from 

 ±0-1 13" to 0-060". Especially important is the fact 

 that although both methods yield abnormal values at 

 times, no systematic difi'erences can be traced. The 

 comparison brings to light an error with the visual 

 instrument that results in a progressive increase of 

 latitude during the night. Dr. Ross is of the opinion 

 that his work substantiates the reality of the Kimura 

 term, and, moreover, proves the existence of " fluc- 

 tuations " not due to a motion of the pole. 



NO. 2432, VOL. 97I 



THE ROYAL OBSERVATORY, GREENWICH. 

 'X'HE report of the Astronomer Royal to the Board 

 ■*■ of Visitors of the Royal Observatory, Green- 

 wich, was read at the annual visitation on Saturday 

 last, J une 3. The report describes the chief observation's 

 and other work carried on at the observatory during the 

 year ending May 10, 1916. The subjoined extracts 

 refer to a few points of particular interest. 



The 28-in. refractor has been throughout the year 

 at the disposition of M. Jonckheere, director of the 

 Lille Observatory, whose observations have been 

 mainly of stars which have been discovered 

 to be double since 1905. He has spent a 

 good deal of time in the identifications and verifica- 

 tions necessary to the completion of the catalogue of 

 double stars referred to in last year's report. During 

 the year 140 new double stars with separation less 

 than 4' have been discovered. 



With the Thompson equatorial photographs have 

 been continued for the determination of stellar parallax 

 in accordance with the programme outlined in last 

 year's report. During the year ended May 10, 1916, 

 a first exposure has been given to 209 plates, and a 

 second exposure, approximately six months after the 

 first, on 226 plates. In the same period 164 plates 

 have been measured, but the measurement has 

 had to be discontinued. During the year thirty- 

 seven photographs have been taken for the 

 determination of the magnitudes of the stars 

 in Kapteyn's selected areas. Of these thirt>'- 

 four have been passed as satisfactory for measurement. 

 Altogether of the ninety fields from declination + 15° 

 to +75°i 149 photographs of fifty-nine fields have 

 been taken. The measurement is well advanced for 

 the plates in zone 15°, but has made very little pro- 

 gress during the year. 



The comparison of the position of stars given in 

 vol. iii. of the Greenwich Section of the Astrographic 

 Catalogue with those given in earlier catalogues for 

 the determination of proper motions has been con- 

 tinued. With the exception of from i2h. to oh. in the 

 zone 65° to 70°, this is practically completed. A 

 search for all stars in the Bonn Diirchmusterung 

 between the pole and declination 64° with large proper 

 motions is in progress by comparison of photographs 

 from sixteen to twenty years apart. Already 200 

 plates with centres at declinations 66°, 68°, 70° have 

 been compared in this way. 



Photographs of the sun were obtained on 244 days. 

 Of these 502 have been selected for preservation, in- 

 cluding thirty-six with double images of the sun for the 

 determination of zero of position angle. The mean 

 dailv spotted area of the sun, which was 152 millionths 

 of the sun's visible hemisphere in 1914, as against 7 in 

 1913, rose in 1915 to considerably over 700 millionths. 



The mean values of the magnetic elements for 

 19 15 and four previous years are as follows : — 



Year 



Horizontal 

 Declination W. Force in 



C.G.S. Units 



191 1 ... 15 33*o ... 018549 



1912 ... 15 24-3 ... 0-18548 



1913 ••• 15 152 ••• 018534 



1914 ... 15 6-3 ... 018518 



1915 ... 14 56-5 ... o 18494 



Dip 



66 52 6 (3-in. needles) 



66 51 46 



66 50 27 

 (66 49 27 

 \ 66 51 13 (dip inductor) 



66 51 58 „ „ 



There were no days of great magnetic disturbance 

 in 1915, but three were classified as of lesser disturb- 

 ance. 



The principal features of interest in the meteoro- 



