146 



NATURE 



[February 2, 1922 



tions of velocity, and not until the Mills spectrograph 

 at the Lick Observatory was got into operation in 

 1 80s by Campbell that thoroughly trustworthy re- 

 sults were obtained. But the earlier observers in the 

 field, as in the parallel case of parallax determina- 

 tions, deserve credit for attacking an important 

 problem, though they did not succeed in overcoming 

 the great difficulties which it presented. _ _ 



On the retirement of Airy, in t88i, Christie was 

 appointed Astronomer Royal. His tenure of office 

 is notable for the large additions he made to the 

 equipment of the Observatory and to the introduction 

 of stellar photography. The first extension of the 

 buildings was an additional computing room, and 

 with it a pier and dome, which served later for the 

 astrographic equatorial. In 1885 he represented 

 to the Admiralty the desirability of increasing the 

 optical means of the Observatory, and received its 

 assent to the purchase of an object-glass of 28-in. 

 aperture and 28-ft. focal length. In co-operation 

 with Stokes an object-glass was proposed which 

 might be used for visual or photographic observa- 

 tions. This telescope, constructed by Sir Howard 

 Grubb, was completed in 1893 and installed on the 

 equatorial mounting which until then had carried the 

 Merz i2|-in. telescope. The drum-shaped dome 

 covering the Merz refractor was worn out, and was 

 replaced by an Oriental -looking dome designed by 

 Christie to contain the longer telescope. This tele- 

 scope was for many years in charge of Mr. Lewis, 

 and has been utilised for a valuable series of obser- 

 vations of double stars. 



The provision of the photographic refractor of 

 13 in. with a lo-in. guiding telescope, to enable 

 Greenwich to take part in the photographic mapping 

 of the heavens, was sanctioned in 1888. The instru- 

 ment, constructed by Sir Howard Grubb, was 

 mounted in the i8-ft. dome over the computing roorns 

 in 1890. The Greenwich section of the astrographic 

 chart and catalogue and the observations of Eros 

 for solar parallax were made with this telescope. 

 Christie took a share in the deliberations and arrange 

 ments for this international undertaking. He de- 

 signed a micrometer for use at Greenwich which faci- 

 litated the comparison of neighbouring plates.^ He 

 was also the discoverer of a very useful empirical 

 formula connecting the magnitude of stars with the 

 diameter of their photographic images. 



The largest, addition to the Observatory was com- 

 menced in 1890, but not completed until 1898. It is 

 a cruciform building, with office rooms on the ground 

 floor, libraries and workshop in the basement, rooms 

 for preserving records and photographs on the upper 

 "floor. The central octagon is used as a store room, 

 and is surmounted by a 36-ft. dome originally built 

 to cover Lassell's 2 -ft. mirror presented to the 

 Observatory by the Misses Lassell. Before the 

 "building was completed Sir Henry Thompson gener- 

 ously offered to provide a 26-in. photographic re- 

 fractor and a 30 -in. reflector, both on the same equa- 

 torial mounting. The equatorial and the refractor 

 were constructed by Sir Howard GrubV) and the 

 mirror by Dr. Common. The refractor was used in 

 •observations of Eros, observations of Neptune's 

 NO. 2727, VOL. 109] 



satellites, and for various other purposes, while the 

 reflector was used in photography of nebulse, obser 

 vations of small planets, comets, faint satellites, 

 etc., and was instrumental in the discovery of the 

 eighth satellite of Jupiter. 



About the same time Christie designed a new 

 altazimuth. The instrument is essentially a transit 

 circle which can be mounted in any azimuth. It re- 

 placed Airy's altazimuth, which did not give suffi- 

 cient accuracy. The new instrument usefully supple- 

 ments the observations of the moon made with the 

 transit circle. 



These various extensions to the Observatory build- 

 ings cramped the space for meteorological observa- 

 tions, and the iron in the domes affected the magnets, 

 which were housed in a wooden building a few yards 

 to the north of the new observatory. A plot of 

 groun^ in Greenwich Park was lent to the Admiralty 

 by the Office of Works, where a magnetic pavilion 

 was erected for taking absolute magnetic ob.serva- 

 tions. 



Christie took a good deal of interest in the obser- 

 vation of total eclipses. He went to Japan in 1896, 

 to India in 1898, to Portugal in 1900, and Tunis in 

 1905. With the equipment arranged by him in 1896 

 an excellent series of large-scale photographs of the 

 corona were taken at the eclipses of 1898, 1900, 

 1901, 1905, and 1914. 



_ Christie retired from his office on his sixty-fifth 

 birthday, October 10, 1910, with the good wishes 

 of his staff. He maintained his interest in the 

 Observatory, and came regularly to the annual visi- 

 tation. He was also frequently at the meetings of 

 the Royal Astronomical Society and the Royal 

 Society, serving on the council of the Royal 

 Society six years and on that of the Royal Astro- 

 nomical Society forty-one years, being president in 

 the years 1 888-1 890. Several foreign academies 

 also accorded him honours. He received the distinc- 

 tion of C.B. on the occasion of Oueen Victoria's 

 Diamond Jubilee and was promoted K.C.B. in 1904. 



He married in 1881 Violette Mary, daughter 

 of Sir Alfred Hickman, of Wolverhampton. Mrs. 

 Christie died in 1888, leaving two sons, one of whom 

 died in childhood. His elder son, Mr. Harold 

 Christie, lived at the Observatory until his father re- 

 tired, when they went to live first at Woldingham 

 and afterwards at Downe. Sir William was of a 

 courteous and hospitable disposition, and would 

 always invite some members of his staff to meet a 

 foreign astronomer who might be visiting the Obser- 

 vatory. He thoroughly enjoyed astronomical con- 

 ferences and eclipse expeditions for the op- 

 portunities they afforded of meeting astronomical 

 colleagues. He acquired in these expeditions a love 

 of sea voyages, and after his retirement made several 

 trips abroad in the winter. In the early part of 

 1 92 1 he went to Jamaica, and paid a visit to Mr. 

 and Mrs. Pickering at the observatory of Mande- 

 ville. This year he started for Mogador a few 

 days after meeting many of his friends' at the Roval 

 Astronomical Society Club. He was then apparently 

 in fair health, but died on January 22, before the 

 ship reached Gibraltar. F. W. Dyson. 



