408 
NATURE 
[JUNE 10, 1915 


THE ROYAL OBSERVATORY, 
GREENWICH.1 
HE Moon’s Tabular Place.—The total number of 
observations made of the moon during the year 
ending May io, 1915, is 107 with the transit-circle and 
98 with the altazimuth, viz. :—64 in the meridian and 
34 extra-meridian. Taking both instruments, observa- 
tions of the moon have been obtained on 127 days 
during the year. 
The mean error in right ascension of the moon’s 
tabular place for 1914 is —o-876s. from meridian ob- 
servations and —o-933s. from extra-meridian observa- 
tions of the moon’s limb, and —o-g15s. from meridian 
observations of the crater Mésting A. The transit 
circle gives —o-899s. Attention is directed tothe great 
increase in recent years of the mean tabular error 
of the moon’s longitude. From 1883, when New- 
comb’s Empirical Correction was introduced into the 
“Nautical Almanac,” the values (all reduced to the 
same equinox) are— 
a“ 

1883 —0-03 | 1899 BBE we = 2-18 
1884 —o-16 | 1900 spr .. — 2:69 
1885 —0-09 | 1901 S60 we 27 
1886 —O-II | 1902 a vas) =) Sus 
1887 +0:21 | i903 S66 we — 3:08 
1888 +076 | 1904 nbc Nes) | Galo 
1889 —038 | 1905 38 w- = 5:20 
1890 —0-27 | 1906 aco we = 5:91 
1891 +0:72 | 1907 500 -. — 5:96 
1892 +079 | 1908 noe we = 5:97 
1893 —0-06 | 1909 is .. — 6-41 
1894 —1-20 | 1910 a5 see Pets 
1895 —1-47 | 1911 ee .. — 834 
1896 —1-68 | 1912 3 — 9:79 
1897 308 me 277 ||| 1913 — 11-93 
1898 cio .- 3-03 | 1914 — 13:0 
Cookson Floating Zenith-Telescope.——During the 
year 238 photographs have been taken, 231 for latitude 
groups and 7 for scale determination. From the com- 
mencement of the observations, 1911, September 7, 
609 latitude plates (excluding rejected plates) have 
been obtained, of which 553 have been measured in the 
direct, and 549 in the reversed position. In addition, 
24 plates taken for scale have been measured and one 
plate rejected. 
The results obtained since the commencement of the 
seven years’ series of observations until the end of 
1914 have been discussed, and the results communi- 
cated to the Royal Astronomical Society. The value of 
the aberration constant obtained is 20-467”+0-006". 
The observations also furnish a determination of the 
latitude variation, although not designed primarily for 
this purpose. The latitude variation derived in this 
way shows a satisfactory agreement with the results 
of the International Latitude Service, and it is hoped 
that a comparison of the two series of results when 
the Cookson results have been brought to a conclusion 
will throw some light upon the origin of the z term 
in the latitude variation. 
The 28-in. Refractor.—Observations of double stars 
have been made from a working catalogue containing 
all known double stars showing appreciable relative 
motion, which are within the range of declination of 
the instrument. A number of other stars are included 
for various reasons, particularly some of those dis- 
covered by Hussey and Aitken under 2” separation. 
Since October 16 M. Jonckheere, the director of the 
Lille Observatory, has also had the use of the instru- 
ment in connection with the catalogue he is preparing 
of double stars of less than 5” separation discovered 
1 From the report of the Astronomer Royal, Sir F. W. Dyson. F.R.S.. to 
the Board of Visitors of the Roval Observatory, Greenwich. Read at the 
_Annual Visitation of the Royal Observatory, on June 5. 
NO. 2380, VOL. 95] 


since 1905, the date of Burnham’s General Catalogue, 
and has carried out many re-measures and verification 
of positions. 
Thompson Equatorial.—The work with this instru- 
ment has been concentrated on stellar parallax and 
photographic photometry. The photographs have all 
been taken with the 26-in. refractor. 
The programme of stars the parallaxes of which are 
being determined contains all those between declina- 
tion+64° and the north pole which are known to have 
a proper motion of more than 20” a century. Each 
star is photographed at times of opposite parallactic 
displacement in right ascension on the same plate. 
It is found that six such plates give a good determina- 
tion. For three of the plates the first exposure is 
given when the star transits soon after sunset and the 
second exposure when it transits a little before sunrise, 
and for the other three the morning exposures are 
made first. Generally, the series of exposures will be 
extended over two or possibly three years, so as to 
avoid anything systematic in observational or instru- 
mental conditions. 
During the year ended May ito, a first exposure has 
been given to 238 plates and a re-exposure to 294. In 
the same period 234 plates have been measured and 
39 in duplicate. Experience seems to show that dupli- 
cate measurement is unnecessary, it being understood 
that each plate contains six images of each star, three 
at each epoch, and that in the first measurement the 
plates are reversed and every image measured twice. 
the parallaxes of 40 stars have been determined, with 
an average probable error of +0009", and the results 
will be communicated to the Royal Astronomical 
Society. 
The determinations of photographic magnitudes 
with the 26-in. refractor have been made by comparing 
certain fields with the polar standards determined by 
Prof. Pickering. Generally, exposures of 6 minutes 
have been made on Ilford ‘‘ Monarch”’ plates, and the 
limiting magnitude reached is about 14-0m. on the 
Harvard scale. During the year 88 photographs of 
this kind have been taken of the ‘selected areas”’ of 
Prof. Kapteyn. 
Six-inch Astrographic Triplet—The catalogue of 
photographic magnitude of stars down to the gth 
magnitude between dec. +75° and +65° has been 
completed and published. It contains 5514 stars the 
magnitudes of which are determined with an average 
probable error of t+o-.06m. The large field of this lens 
makes it very suitable for the determination of the 
photographic magnitudes of the brighter stars, and it 
is hoped to carry on this work in other declinations 
as opportunity offers. 
Astrographic Equatorial—The observing has con- 
sisted mainly of chart plates for the Oxford zone dec. 
+25° to +31°. Two exposures of 30 minutes each 
are given to each field, Wellington ‘‘ Xtreme” plates 
being used on account of their speed. 
The printing of vol. iii. of the Astrographic Cata- 
logue was finished in August. This volume contains 
the right ascensions and declinations, as well as the 
photographic magnitudes, of 16,780 stars from declina- 
tion +64° to the north pole deduced from the measure- 
ments of the astrographic plates. 
A thorough examination of these stars for the deter- 
mination of proper motion is being carried out, and 
in addition to the catalogues mentioned comparisons 
are being made with the observations of Lalande, 
Argelander, and others. Proper motions have been 
determined for the stars of Carrington’s Catalogue 
(dec. 81° to the pole), of the Kasan Catalogue (dec. 
75° to 80°), and of the Dorpat Catalogue (dec. 70° 
to 75°) as far as 18h. In a number of cases large 
proper motions have been verified by comparison of 
