June 8, 1899] 
NATURE 137 
graphic records and books of calculations, and for the library, 
which had long outgrown the rooms hitherto available for it. 
In the new Observatory building—which is cruciform in shape, 
having four wings of three stories, with a central tower carrying 
the Thompson equatorial and dome—the staff occupies the 
principal floor, the library will be placed in the ground floor of 
the north, east and west wings, the ground floor of the south 
wing being fitted up as a workshop, and the upper floor will ac- 
commodate the photographic and other records and the stock of 
publications of the Observatory. Mr i 
The completion of the new Observatory building, which at 
three points breaks into the existing boundary fence, makes it 
desirable that the boundary of the Observatory should be en- 
larged in order to show off the handsome new building, and a 
proposal to give effect to this is under the consideration of the 
Admiralty. , 
The new Magnetic Pavilion, in an enclosure in Greenwich 
Park, at a distance of about 350 yards from the Observatory, on 
the east side, was completed at the end of last September, and 
the magnetic instruments for absolute determinations have been 
installed there. The greatest care has been taken to exclude all 
iron in building the Magnetic Pavilion, and the site has been 
selected so that there is no suspicion of magnetic disturbance 
from iron in the neighbourhood. The enclosure also providesa 
good meteorological station, where the standard thermometers 
and rain-gauges have been mounted. 
Transit Circle. 
The sun, moon, planets, and fundamental stars have been 
regularly observed on the meridian as in previous years. The 
number of observations made from 1898 May 11 to 1899 May 
10, was as follows :— 
Transits, the separate limbs being counted as 
one observation é oa oo 11,764 
Determinations of collimation error ... 208 
Determinations of level error ... 6904. 
Circle observations ie Fer, FA PeELO; O30 
Determinations of nadir point (included in the 
number of circle observations) eh ae 665 
Reflection observations of stars (similarly in- 
cluded) 5 Pe cen 560 
The number of stars observed in 1898 was about 5000. 
The number of meridian observations in the first three months 
of 1899 was unusually large, being 1200 more than the average 
of the three preceding years. The excess was entirely in 
January and February, for which months the number of observ- 
ations was double the average number. This unusually large 
number of observations has caused great pressure on the com- 
puting staff in that branch, and it is much to their credit that the 
reductions have fallen so little behind. 
The apparent correction for discordance between the nadir 
observations and stars obtained by reflection for 1898 was found 
to be - 0”°36. The results of recent years are as follows :— 
Mean Range 
———— 
1880-1885 - 0°34 from. — 06°29 to -0°45 
1886-1891 +0°03 from —0'12 to +009 
1892-1898 —0°30 from —0-25 to —0°36 
New steel screws for the microscope micrometers were intro- 
duced in 1886, and in October 1891 the object-glass was 
repolished, and a new steel telescope micrometer screw was 
introduced. 
Both microscope and telescope micrometer screws have been 
examined, but show no errors which would account for this 
discordance. 
The co-latitude of the transit-circle, as found from observations 
of about 600 stars in 1898, is 38° 31 21''°75, differing by, —o”:15 
from the adopted value. The effect of Chandler’s latitude vari- 
ation was computed for each of these stars within the limits 10° 
and 35° N.P.D. The table, which is given in the Report, 
exhibiting the effect of Chandler’s correction to the colatitude on 
the means of groups arranged for each hour of right ascension, 
shows how entirely its influence is eliminated from the resulting 
co-latitude. 
The mean error of the moon’s tabular place (computed from 
Hansen's lunar tables with Newcomb’s corrections) is — 0°143s. 
in R.A. and +0"14 in N.P.D. deduced from 104 observations, 
NO. 1545, VOL. 60] 
These are equivalent to an error of —2’’'23 in longitude and 
+021 in ecliptic north polar distance. 
In the last Report, the equivalent error in longitude was — 1°97 
and +0"°16 in ecliptic north polar distance. 
From June to December 1898 a new determination of the 
division errors of the transit-circle was made by Mr. Dyson and 
Mr. Thackeray. An account of this investigation has been 
published in the AZemozrs of the R.A.S., vol. liii., so that we 
need not refer again to it here. 
The New Altazimuth. 
After the date of the last Report, it was found that the read- 
ings of the several microscopes varied systematically with the 
direction in which the instrument was swung. As this pointed 
to a constraint in the axis, several modifications were made in 
different parts of the instrument. These various changes were 
not completed till February 23, and since then the observations, 
both of transits and zenith distances in reversed positions, show 
a satisfactory accordance. 
Among the observations made with this instrument may be 
mentioned 1017 R.A. observations of the sun, planets and stars, 
961 N.P.D. observations of the same bodies, and 20 observations 
in R.A. and N.P.D. of the moon. 
Thompson Equatorial. 
The return of the object-glass of the 26-inch refractor on 1898 
May 16 is referred to in the last Report. Slight figuring of the 
outer surface under Sir Howard Grubb’s direction was con- 
tinued till June 8. The object-glass was further tested by 
photographs taken inside and outside of focus and with dia- 
phragms, and was finally approved in September. The new 
30-inch mirror, of slightly shorter focal length (corresponding 
to the length of the tube), was received from Dr. Common on 
September 1. Photographs to test the mirror were taken in 
the principal focus and also in the secondary focus, and it was 
found to be quite satisfactory. 
With the 26-inch refractor, twelve successful photographs of 
Neptune and its satellite have been obtained, using the occult- 
ing shutter to screen the planet during the greater part of 
the long exposure necessary to show the satellite, a series of 
short intermittent exposures for the planet being given by lifting 
the arm of the shutter. The results of these observations 
are given in the Monthly Notices vf the Royal Astronomical 
Soctety, vol. lix., May. Forty-two successful photographs of 
sixteen double stars have also been obtained, including six of 
Aldebaran, for which the occulting shutter was used in order to 
obtain measurable images of Aldebaran and the faint companion, 
for which a 20m. exposure was required. A few photographs 
of fields of stars have also been obtained. 
With the reflector, thirty-two photographs of the planet Eros 
were obtained between September 20 and March 31, nine 
photographs of Neptune and its satellite, four of Comet Brooks, 
and one of Comet Tuttle. To investigate the distortion of the 
field, five photographs of the Pleiades have been taken. 
With an exposure of an hour, a ‘‘fine photograph of the 
Andromeda nebula has been obtained.” 
28-z2nch Refractor. 
This instrument has been used throughout the year for micro- 
metric measurements of double stars. Four hundred and ten 
stars have been measured ; 206 of these have their components 
less than 1’o apart, and 87 less than 0”’5. The stars the 
distance apart of which is less than 1’’°0 have been measured on 
the average on three nights each, and the wider pairs on twoand 
a half nights. The wider pairs measured consist of stars in 
which there is a considerable difference of magnitude between 
the components, of third companions to close pairs, and of stars 
which are of special interest. 
A long series of measures of 70 Ophiuchi has been obtained. 
Astrographic Equatorial. 
During the year ending 1899 May 10, 465 plates have been 
taken on 120 nights. Of these 78 have been rejected, viz. 34 
because the exposure was interfered with by cloud, or because 
the images were too faint to show 9th magnitude stars with a 
20s. exposure ; 17 owing to faults in guiding or exposure ; 8 on 
account of wrong setting ; and 19 from miscellaneous defects. 
The following statement shows the progress made with the 
photo-mapping of the heavens :— 
