136 



NA TURE 



[June 8, 1905 



ations, loo requiring two, and 1500 requiring one observ- 

 ation only in order to carry out the programme. In fact, 

 it may be taken that the observations for this catalogue 

 are practically completed. The catalogue, which will be 

 terminated this year, will contain, besides the reference 

 stars for the Astrographic Catalogue, the 834 zodiacal 

 stars given in the Nautical Almanac for 1897. 



It is proposed to begin next year a new nine-year cata- 

 logue of the stars of magnitude 90 and brighter between 

 the limits -1-24° to -1-32° of N. declination, this being the 

 Oxford astrographic zone, for which they serve as refer- 

 ence stars. The re-observation of these stars, which for 

 the most part fall within the Cambridge zone of the 

 Astronomische Gesellschaft Catalogue, will afford valuable 

 data for their proper motions, besides giving fundamental 

 positions for the Oxford astrographic plates. 



The comparison between theory and the Greenwich 

 meridian observations of the moon from 1750 to the present 

 time, undertaken by Mr. Cowell, has been completed for 

 the longitudes, and the discussion from 1847 to 1901 is 

 completed for the latitudes. The only point left outstand- 

 ing is the motion of the node, for which it is necessary 

 to discuss as long a series of observations as possible. 

 The results obtained for the longitudes are summarised in 

 a series of papers in the Monthly Notices of the Royal 

 Astronomical Society. In particular, the paper in vol. 

 Ixv., No. 2 (1904 December), gives the coefficients of 145 

 terms as obtained directly from observation, with a com- 

 parison with the theoretical coefficients given by Hansen, 

 Delaunay, M. Radau, and Dr. Hill. The publication of 

 the details of the whole investigation will be shortly 

 proceeded with. 



The re-reduction of Groombridge^s observations was 

 completed at the date of the last report, and during this 

 year the printing of the results has been pushed on. The 

 introduction has also been prepared for press. A dis- 

 cussion of the proper motions determined li)y comparison 

 with modern Greenwich observations, and a determination 

 of the constant of precession and of the direction of the 

 solar motion by Mr. Dyson and Mr. Thackeray, are given 

 in the Monthly Notices of the Royal Astronomical Society, 

 March. 



The altazimuth has been in regular use throughout the 

 year, and a second determination of the pivot errors has 

 been made, and also observations for obtaining the value 

 of one revolution and errors of the screw of the telescope- 

 micrometer have been completed. 



The observations of the moon, both in and out of the 

 meridian, seem very satisfactory as shown by the agree- 

 ment between the two instruments, the transit circle and 

 the altazimuth. 



The 28-inch refractor has been employed, as was the 

 case last year, for micrometric measurements of double 

 stars, the total number measured being 603. Of these, 143 

 have their components less than i"o apart, and 60 less 

 than o"-5. A marked deterioration of the images of the 

 stars led to an examination of the lenses, and the suspected 

 tilt between the components was corroborated and 

 remedied. 



Sixty-five photographs of Neptune and its satellite have 

 been secured with the 26-inch refractor, while, with the 

 30-inch reflector, numerous photographs of minor planets 

 and comets a, b, c 1904, and a 1905, have been obtained. 



At the date of the last report, 119 plates taken of Eros 

 with the astrographic equatorial, and 55 taken with the 

 Thompson equatorial, had been measured. During this 

 year the remainder of the photographs have been measured, 

 making in all 198 with the astrographic equatorial and 

 152 with the Thompson instrument. The reduction of the 

 measures is in a satisfactory state, and it is expected that 

 it will be completed in two months for both sets of 

 photographs. 



The astrographic equatorial has been employed mainly 

 to obtain photographs to replace chart plates which show 

 slight photographic defects unsuitable for production of 

 enlarged prints. 



The measurement of the catalogue plates for the Green- 

 wich section is now completed. Since the last report 

 47,200 measures of pairs of images (6m. and 3m.) have 

 been made. The number of plates measured in the year 

 is 102, covering 128 square degrees between declination 

 NO. 1858, VOL. 72] 



83° and the pole. The number of plates measured up to 

 the date of last year's report was 1051. Adding the 102 

 plates measured this year, the total number of plates 

 measured is 1153, being the 1149 of the Greenwich section 

 + 4 additional photographs of the polar field. 



For the year ending 1904 December 31, Greenwich photo- 

 graphs of the sun have been selected for measurement on 

 209 days, and photographs from India and Mauritius (to 

 fill up the gaps in the series) on 151 days, making a total 

 of 360 days out of 366 on which photographs are at 

 present available. Photographs were taken in Mauritius 

 for three of the si.x days yet unrepresented, and may be 

 received in due course. 



The solar activity has shown a great increase during 

 the year ending 1905 May 10, and the sun has not been 

 free from spots on a single day during that period. The 

 mean daily spotted area for 1904 was more than half as 

 great again as that for 1903, and early in the present year 

 a number of exceptionally large groups was observed. 

 The group which was seen first on the east limb on 1905 

 January 28 had a greater total area than any other group 

 which has been photographed at the Royal Observatory. 



The principal results of the magnetic elements for 1904 

 are as follows : — 



16° 15' o West. 

 ( 4'Ol66 (in British Units). 

 \ I '8520 (in Meliic Units). 



66° 57' II". 



Mean declinalion 



Mean horizontal force ... 



Mean dip (with 3 needles) 



In 1904 there were no days of great magnetic disturbance 

 and eight of lesser disturbance. 



The mean temperature for the year 1904 was 49°-8, or 

 o°-3 above the average for the fifty years 1841-90. During 

 the twelve months ending 1905 April 30 the highest 

 temperature in the shade (recorded on the open stand in 

 the magnetic pavilion enclosure) was gi^'O, on August 4. 

 On the same day the highest temperature in the Stevenson 

 screen in the magnetic pavilion enclosure was 89°-5, and 

 in the observatory grounds 89°-7. The lowest temperature 

 of the air recorded in the year was i9°-5, on January i. 

 During the winter there were thirty-nine days on which 

 the temperature fell below 32°o, being seventeen less than 

 the average number. 



The mean daily horizontal movement of the air in the 

 year ending 1905 April 30 was 280 miles, which is 2 miles 

 below the average of the preceding thirty-seven years. 

 The greatest recorded daily movement was 867 miles, on 

 November 9, and the least 49 miles, on December 22. 

 The greatest recorded pressure of the wind was 235 lb. 

 on the square foot, on March 12, and the greatest hourly 

 velocity 45 miles, on December 30. 



The number of hours of bright sunshine recorded during 

 the twelve months ending 1905 April 30, by the Campbell- 

 Stokes instrument, was i486 out of 44^7 hours during 

 which the sun was above the horizon, so that the mean 

 proportion of sunshine for the year was 0333, constant 

 sunshine being represented by i. 



The rainfall for the year ending 1905 April 30 was 

 2021 inches, being 433 inches less than the average of the 

 fifty years 1841-90. The number of rainy days was 153. 

 This small rainfall may be contrasted with the heavy 

 rainfall of 3542 inches in the corresponding period last 

 year. The most striking contrast is obtained by com- 

 paring the rainfall for the year commencing 1903 March i, 

 which was more than 37 inches, with that for the year 

 commencing 1904 March 1, which was less than 17^ 

 inches. This dry period of twelve months was followed 

 by a heavy rainfall in 1905 March, which exceeded 3J 

 inches, and is the greatest amount recorded in March since 

 1851. 



The printing of the Paris-Greenwich longitude deter- 

 mination, 1902, is practically complete. The Killorglin 

 longitude is the only determination which still requires to 

 be printed to complete the volume of longitude determin- 

 ations, which will contain the determinations Paris-Green- 

 wich made in 1888, 1892, and 1902, of Greenwich- 

 Waterville-Canso-Montreal made in 1892, and of Green- 

 wich-Killorglin made in 1898. 



The re-reduced Groombridge Catalogue is nearly com- 

 pletely printed, with the exception of the introduction, 

 which is ready for the press. 



