June lo, 1897] 



NATURE 



135 



!i;ind, and the former was soon satisfactorily effected. For the 

 • Ijustment of the object-glass a number of photographs have 

 1 leen taken inside and outside of the focus, the separation between 

 I he lenses being varied with a view to the correction of the small 

 outstanding aberration and coma. Some photographs of the 

 moon and of double stars have been taken, an enlarging camera 

 with a Dallmeyer concave magnifier being applied to the tele- 

 scope in some cases to give a magnified image. This equatorial 

 carries not only the 26-inch photographic telescope with the 

 I2ij-inch Merz guiding telescope and the Thompson 9-inch 

 photoheliograph, but also a Cassegrain reflecting telescope of 30 

 inches aperture with the 6-inch Hodgson telescope as guider in 

 place of the counterpoise at the other end of the declination 

 axis. It thus provides a very powerful combination of tele- 

 sctjpes specially adapted to photographic work of various kinds, 

 and special arrangements in the instrument and observing room 

 have been necessary to meet the varied requirements. The 

 instrument has now been got into good working order, and is 

 very satisfactory as regards the mechanical arrangements. The 

 photographic spectroscope will be used in connection with the 

 Cassegrain reflector mounted firmly at the back of the cell of 

 the mirror, a diagonal prism being used to reflect the rays into 

 the collimator. 



The 1%-inch Refractor. 



This instrument was in constant use for micrometric measure- 

 ments from 1896 May 11, to 1897 January 11. On January 12 

 the crown lens was reversed, and the instrument used for 

 photography till April 23, except on the occasion of Prof. 

 Barnard's visit to the Observatory, when the lens was replaced 

 in the visual position. Besides several micrometric observations, 

 195 double stars were measured during the year ending May 10. 

 The distance and position-angle of the satellite of Neptune were 

 measured on four nights, and the equatorial and polar diameters 

 on two nights. The equatorial and polar diameters of Mars 

 were measured on seven nights. With the crown lens in the 

 reversed position, a number of photographs was taken in and 

 out of focus for the better adjustment of the separation of the 

 lenses and the tilt. 



The Asirophysical Equatorial. 



The following statement shows the progress made with the 

 photo-mapping of the heavens : — 



For the Chart For the Catalogue 

 (exposure 40m.). (exposures 6in., 3m. 

 and 20s.). 

 Number of photographs taken 175 ... I39 



,, successful plates ... 135 ... no 



,, fields photographed 



successfully 133 ... 98 



Total number of successful fields 



reported 1896, May 10 ... 490 ... 732 



Number of photographs, pre- 

 viously considered success- 

 ful, rejected during year ... 72 ... 16 



Total number of successful fields 



obtained to 1897 May 10 ... 551 



814 



Number still to be taken ... 598 ... 335 



Of the fields still required 197 are within 10° of the Pole, and 

 no photographs of this part of the sky have yet been taken, the 

 work being purposely deferred till near the epoch 1900. 



Spectroscopic and Heliographic Observations. 



Photographs of the sun were taken on 222 days, and of these 

 471 have been selected for preservation, besides twelve photo- 

 graphs with double images of the sun for determination of zero 

 : position-angle. 



For the preceding year Greenwich photographs were selected 

 for measurement on 206 days, and photographs from the Solar 

 Physics Committee (filling up the gaps in the series) on 154 days, 

 making a total of 360 days out of 366 on which photographs are 

 available. 



The spot activity of the sun has continued on the whole to 

 decline since the date of the last Report, but has undergone two 

 remarkable cases of temporary revival ; the one in September 

 1896, when the longest connected group ever photographed at 

 Greenwich was observed, and the other at the commencement 

 of the present year. On the other hand, the sun was seen to be 

 free from spots on six days in the year ending 1897 May 10. 



NO. 1441, VOL. 56] 



Maptetic Observations. 



The variations of magnetic declination, horizontal force and 

 vertical force, and of earth currents have been registered photo- 

 graphically, and acccompanying eye observations of absolute 

 declination, horizontal force and dip have been made as in 

 former years. 



The principal results for the magnetic elements for 1896 are 

 as follows : — 



Mean declination ... 16" 56'"5 West. 

 Mean horizontal force (^'f 34 (in British units). 

 ' '8367 (m metric units). 



Mean dip 



[bf 8' 



... Uf 9' 



^67° 10' 



■5 (by 9-inch needles). 

 3 (by 6-inch needles), 

 o (by 3-inch needles). 



These results are to a certain extent afiected by the iron in the 

 new Physical Observatory, and in the new Altazimuth Pavilion, 



The selection of the site for the new Magnetic Pavilion re- 

 quired much consideration and necessitated observations at a 

 number of stations in Greenwich Park. As the result of the survey 

 it was decided to abandon a site which had been provisionally 

 selected at a distance of about 250 feet to the east of the reser- 

 voir, and to choose another at a considerably greater distance 

 both from the reservoir and the Observatory. 



Meteorological Observations. 



The mean temperature of the year 1896 was 50°' i, being o'v 

 above the average for the fifty years 1841-1890. 



During the twelve months ending 1897 April 30, the highest 

 daily temperature in the shade recorded on the open stand was 

 9i°*i on July 14. The highest reading recorded in the Stevenson 

 screen was 87° "6. Under the same conditions of exposure on 

 the open stand there have been twenty-six instances of tempera- 

 tures exceeding 90° recorded in the preceding fifty-five years, the 

 highest having been 97° 'i on 1881 July 15. The temperature 

 rose twice above 90° in 1896, and seventeen times above 80°. 

 The monthly mean temperatures for June, July, February and 

 March were respectively above the corresponding averages by 

 4°*o, 2" "8, 3° "5 and 3° '3 ; and the means for August, October, 

 November and January were in defect by 2° "5, 3''*5, 2° 7 and 

 3"'i. The mean temperature for the twelve months 1896 May 

 to 1897 April was 49°7, being o°2 above the fifty years' 

 average. 



In the winter months of 1896-1897 there were forty-two days 

 on which the temperature of the air fell to the freezing-point, or 

 below ; sixteen of these days occurring in January, and eleven in 

 December. The lowest winter temperature was 23° "8 on 1897 

 January 18, as compared with 24° "3 in the preceding winter. 



The number of hours of bright sunshine recorded during the 

 twelve months ending 1897 April 30 by the Campbell-Stokes 

 instrument (with the old ball up to December 31, and with the 

 new ball after), was 1 152 out of the 4454 hours during which the 

 sun was above the horizon, so that the mean proportion of sun- 

 shine for the year was 0*259, constant sunshine being represented 

 by I. This amount is probably too small for reasons stated in 

 the report. 



The rainfall for the year ending 1897 April 30 was 26 83 

 inches, being 2*29 inches above the fifty years' average. The 

 number of rainy days in the twelve months was 178. 



Personal Establishment. 



In the last Report mention was made regarding the reorganisa- 

 tion of the stafi". The arrangement now adopted is that Mr. 

 Dyson and Mr. Cowell have the general superintendence of all 

 the work of the Observatory, Mr. Dyson taking special charge of 

 the astronomical department, and Mr. Cowell of the astro- 

 physical department, in which is included the magnetic and 

 meteorological branch. Mr. Maunder is charged with the 

 heliographic photography and reductions. Mr. Lewis has charge 

 of the time-signals and chronometers, and of the 28-inch 

 equatorial. Mr. Thackeray superintends the miscellaneous 

 astronomical computations and meridian zenith-distance re- 

 ductions. Mr. Hollis has charge of the photographic mapping 

 of the heavens, the measurement of the plates, and the compu- 

 tations for the astrographic catalogue. Mr. Crommelin under- 

 takes the altazimuth and Sheepshanks equatorial reductions, 

 and Mr. Bryant the transit-reductions and time-determinations. 

 In the magnetic and meteorological branch, Mr. Nash has the 

 charge of the whole of the work. 



