234 



NATURE 



[July 5, 1900 



The results of recent years are as follows : — 



Mean Range in Yearly Means 



P'rom -0'29 to -0*45 



„ -0'12 to +0*09 



,, -0-25 to -0-36 

 Observations of level and nadir have been made, when prac- 

 ticable, three or more times on the same day, and diurnal 

 changes similar to those referred to in the last report have been 

 found in 1899. The observations of level taken within three 

 hours of noon and midnight give corrections of +o""30 and 

 + o"'i8 respectively, to those made within three hours of 6 p.m. 

 Similarly the observations of nadir near noon and midnight 

 give corrections of +o"-i7 to those made within three hours of 

 6 p.m. 



In view of this systematic diurnal movement of the instrument 

 and of the large number of observations of azimuth stars in 

 recent years, it seems probable that the limit of accuracy obtain- 

 able by the use of double transits for the determination of the 

 positions of the close polar stars has been reached, as this 

 involves the assumption that the azimuth error remains constant 

 for twelve hours at least. It has therefore been arranged to use 

 these stars for determination of azimuth error, by means of their 

 tabular right ascensions, and to keep the observations for im- 

 provement of the tabular place only when the azimuth error has 

 been determined by at least three pairs of close polar stars above 

 and below pole on the same evening. 



The correction for the R-D discordance, found for 1899, is 

 -f o"-o8o-fo"'2i8 sin Z.D. The coefficient of sin Z.D. was 

 about -f o" 6 from 1881 to 1894, diminished to 4- o"*4i and 

 -fo"-37 in 1895 and 1896, to -fo"-io in 1897 and 1898, and 

 has now increased to +o"'22. 



The observations of the zenith distances of pairs of stars 

 directly and by reflexion, alternately on alternate nights, have 

 been discontinued. The observations made in the four years, 

 1895, 1S96, 1897 and 1898, show a satisfactory agreement with 

 the ordinary observations, reflexion and direct at the same 

 transit, confirming the striking diminution in the value of the 

 R-D discordance in 1897 and 1898 as compared with 1895 and 

 1896. 



The colatitude of the transit circle, as found from observa- 

 tions of about 600 stars in 1899, is 38° 31' 2i"76, differing by 

 -o""i4 from the adopted value. The corresponding values of 

 the correction to the adopted colatitude found in 1897 and 1898 

 are - o"-i7 and -o"'i5, and it may be noticed that the R-D dis- 

 cordance was very small in these years. 



The mean error of the moon's tabular place (computed from 

 Hansen's lunar tables with Newcomb's corrections) is -o5"099 

 in R.A. and -l-o"-27 in N. P. D., deduced from 116 observations. 

 These are equivalent to an error of - i"'38 in longitude and 

 o''00 in ecliptic north polar distance. 



The re-observation of the stars of Groombridge's Catalogue, 

 which was the principal object of the Second Ten-Year Cata- 

 logue, furnishes material for determination of the proper 

 motions of more than 4000 stars from observations about eighty 

 years apart, with intermediate positions in the Radcliff"e Cata- 

 logue of 1845. Provisional proper motions are given in the 

 Introduction for 163 stars, for which the annual proper motion 

 in R.A. or N. P.D. amounts to o"'i of a great circle, and had 

 not previously been determined. It is proposed to undertake 

 the determination of the proper motions of all the stars in 

 Groombridge's Catalogue. Before doing this it was considered 

 desirable to re-examine Groombridge's Observations, with 

 special reference to the determination of azimuth error, in 

 view of the large systematic error in Right Ascension. The 

 original MSS. of Groombridge's Observations have been kindly 

 lent by the Council of the Royal Astronomical Society, and the 

 examination is in progress. 



The New Altazimuth. 

 This instrument is now in good working order. Various re- 

 pairs have been required and minor improvements have been 

 made. The observations of transits seem quite satisfactory, the 

 accordance in the results for clock error in diff'erent positions of 

 the instrument (referred to the transit circle) being very good. 

 For the zenith distance observations further determinations of 

 flexure and division-errors are required, and these are in hand. 

 The investigation of the division errors of both circles has shown 

 that the accordance of two determinations is not very satis- 

 factory, and the cause of the discrepancy is now under investiga- 

 tion. 



• NO. 1 601, VOL. 62] 



Among the observations made with this instrument may be 

 mentioned 1729 R.A, observations of the sun, planets and stars, 

 1418 N. P.D. observations, and 2386 observations for collima- 

 tion, level, and azimuth errors, and nadir. 



The 28-INCH Refractor. 



This instrument has been used throughout the year for micro- 

 metric measurements of double stars. 492 stars have been 

 measured ; 268 of these have their components less than i"o 

 .apart, and 139 less than o"-5. The stars whose distance apart 

 is less than i"-o have been measured on the average on three 

 nights each, and the wider pairs on two nights. The wider 

 pairs measured consist of bright stars with a faint companion, of 

 third companions to close pairs, and of stars of special interest. 



In consequence 'of Mr. Newall's suggestion that the newly 

 discovered spectroscopic binary Capella might possibly be ob- 

 served as a double star with large telescopes, it has been ex- 

 amined on fifteen nights (from April 4 to May 10) by a number 

 of observers, who all found the star's image to be sensibly elon- 

 gated ; while the position angle of the elongation changed 

 during the period of observation (April 4 to May 29) in fair 

 accordance with the period of 104 days given by Mr. Newall. 



Thompson Equatorial. 



The 26-inch refractor has been in constant use throughout 

 the year. The occulting shutter has been found of great value 

 in obtaining accurately measurable photographs when one of the 

 objects photographed is considerably brighter than the other 

 objects in the field. 



Fifteen photographs of Neptune and its satellite have been 

 obtained, of which seven have been measured. Fifty-four 

 photographs of twenty-six double stars have been obtained, of 

 which forty-seven have been measured. Among these stars are 

 Algol and Aldebaran, with their faint companions of fourteenth 

 magnitude. The measures of distance and position-angle of 

 the photographs of double stars are published in the Monthly 

 Notices of the Royal Astronomical Society for April 1900 

 Nineteen photographs have been obtained of Comet Swift, of 

 which fifteen have been measured, and the results published in 

 the Astronouiische Nachrichlen, Nos. 3584-5. In addition, 

 photographs of Polaris and neighbouring stars have been taken 

 for parallax, a few photographs of the moon and some of the 

 major planets with their satellites, and others for testing ad- 

 justments and the characters of the images in different parts of 

 the field. 



The 30-inch reflector has been used chiefly for the photo- 

 graphy of nebulse and star clusters. The photographs of the 

 nebulosity of the Pleiades and of the Orion nebula are very 

 fine, and show a large amount of detail. 



Astrographic Equatorial. 

 The following statement shows the progress made with the 

 plates for the chart and the catalogue respectively : — 



For the Chart For the Catalogue 

 (exposuie (exposures 6m., 



40m.). 3m., and 20S.). 



Number of photographs taken ... 243 ... 236 

 ,, successful plates ... 162 ... 181 



,, fields photographed 



.successfully ... 155 ... 175 



Total number of successful fields 



reported 1899 May ID 1027 



Number of photographs, previously 

 considered successful, rejected 

 during the year ... ... ... 106 ... 102 



Total number of successful fields 



obtained to 1900 May 10 ... 1076 ... 1x03 



Number still to be taken ']t^ ... 46 



A comparison of this list with the one published in the last 

 report shows that great progress has been made in this work. 



It is satisfactory to note that the plates are now placed in 

 the new observatory, where they are kept dry and not subject 

 to the extremes of temperature as formerly. Those that were 

 previously spoilt through damp are now being gradually 

 replaced. 



During the year 88,000 measures of pairs of images (6m. 

 and 3m.), as well as of the diameters of the 6m. images, have 

 been made. The number of quarter plates measured in the 

 twelve months in two positions of the plates is 556. 



1030 



