yune 10, 1886] 
NATURE 
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definition of the collimator object-glasses should be 
thoroughly tested. 
A discussion of the collimation-observations made 
throughout the year 1885 with the reversion-prism shows 
that for the regular observers the personality depending 
on the apparent direction of measurement is extremely 
small. Any possible effect of the kind is eliminated by 
-the method of observation adopted with the reversion- 
prism. The personality depending on the direction of 
motion, as deduced from the results of reversed and 
ordinary transits of clock-stars with the reversion-prism, 
appears to be more decided, though the amount is small 
except in the case of one observer. 
The personal equation instrument was completed last 
autumn, but was dismounted during the winter to preserve 
it from injury in the bad weather. Series of observations 
have been taken with it on five days, and the results 
appear to be very satisfactory, the accordance being as 
close as could be expected. The absolute personal equa- 
tions thus obtained seem to show that all the observers 
observe too late, the differences between the several 
observers agreeing well with the relative personal equa- 
tions found from observations of clock-stars. 
The sun, moon, planets, and fundamental stars have 
been regularly observed during the past year, together 
with other stars from a working catalogue containing 
about 2750 stars. Good progress has been made in the 
observation of these stars, in view of the formation at the 
end of 1886 of a Ten-Year Catalogue, epoch 1880’0. The 
annual catalogue of stars observed in 1885 contains about 
1250 stars. 
The following statement shows the number of observa- 
tions made with the transit-circle in the tweive months 
ending 1886 May 20 :— 
Transits, the separate limbs being counted as separate 
observations S09 ocd Sc 5685 
Determinations of collimation error ... 306 
Determinations of level error ... 332 
Circle observations ee +6 ae Pron sy h5) 
Determinations of nadir point (included in the 
number of c rele-observations) 5p Be ban ae SUS 
Reflection-observati ns of stars (similarly included) 530 
The value found for the co-latitude from the observations 
of 1885 is 38° 31' 22’04, differing by o14 from the 
assumed value; the correction to the tabular obliquity of 
the ecliptic is + 0”°81 ; and the discordance between the 
results from the summer and winter solstices is — 0’ 98, 
indicating that the mean of the observed distances from 
the pole to the ecliptic is too great by + 0''49. 
The mean error of the moon’s tabular place (computed 
from Hansen’s Lunar Tables with Prof. Newcomb’s cor- 
rections) is + o’02s. in R.A. and + 0°36 in longitude, as 
deduced from 105 meridian observations in 1885. The 
mean error in tabular N.P.D. is — 0°58, which would 
appear to agree with the observations of the sun in indi- 
cating that the mean of the observed N.P.D.’s is too 
great. 
The observations of the moon with the altazimuth 
have, as usual, been restricted to the period from last 
quarter to first quarter in each lunation, the total number 
of observations of various kinds made in the twe!ve months 
ending 1886 May 20 being as follows :— 
Azimuths of the moon and stars ... 
21 
Azimuths of the azimuth-mark ae 
Azimuths of the collimating-mark 176 
Zenith-distances of the moon oat con 110 
Zenith-distances of the collimating-mark 172 
The reversion-prism has been used during the past 
year with the altazimuth for investigation of the person- 
ality depending on the apparent direction of motion of 
stars or the moon. The plan adopted has been to 
observe a transit over the first three wires with a certain 
apparent direction of motion and over the last three with 
the apparent direction of motion changed. A second 
transit is then observed with the conditions reversed, so 
that in each double transit there are two sets of observa- 
tions over the same six wires with the apparent direction 
of motion different, from which a determination of the 
personality is obtained by simple subtraction without any 
calculation of intervals of wires. The results show that 
the personality is in every case small, and that further 
observations are required to separate it from accidental 
errors of observation. 
A clock synchronised by hourly currents, on Lund’s 
system, has been presented to the Observatory by the 
Standard Time and Telephone Company, and is fixed in 
the Astronomer-Royal’s office. 
A new plane mirror (silver on glass) has been obtained 
from Mr, Calver for the Lassell equatorial, and a wooden 
screen has been fixed at the eye-end to protect the open 
end of the tube from the heat of the observer's body, it 
having been found that the definition was much affected 
by convection-currents at the eye-end, giving rise to an 
apparent astigmatism which was at first supposed to be 
caused by tilt of the large mirror. The optical_perform- 
ance appears now to be satisfactory. At Mr. Common’s 
suggestion a frictional connection between the clock and 
the driving-screw has been applied so as to allow of the 
latter being turned in either direction (for slow motion in 
R.A.) without putting the clock out of gear. 
For determination of motions of stars in the line of 
sight, 378 measures have been made of the displacement 
of the F line in the spectra of 51 stars, and 21 measures 
of the 2 lines in 8 stars, besides measures of the displace- 
ments of the d and F lines in the spectra of Mars and 
Venus, and of the east and west limbs of Jupiter, and 
comparisons with lines in the spectrum of the moon, or 
of the sky, made in the course of each night’s observa- 
tions of star-motions, or on the following morning, as a 
check on the general accuracy of the results. The ob- 
servations of Sirius during the past twelve months indi- 
cate, as in the last three years, a displacement of the I 
line towards the blue (corresponding to a motion of ap- 
proach), the amount being slightly larger than in the pre- 
ceding year. Spectroscopic observations were interrupted 
on a number of nights through deficient supply of water 
for the driving-clock of the south-east equatorial. After 
some correspondence with the Kent Waterworks Com- 
pany it was arranged that the pressure in the Observatory 
main should not be reduced to so low a point in the 
evening, and no further trouble with the water supply has 
been experienced since. The experiments with the re- 
version spectroscope of the Oxford University Observa- 
tory (lent by Prof. Pritchard) indicate that this form of 
instrument is well adapted for observation of displace- 
ments, provided certain improvements can be effected in 
the optical and mechanical parts. 
For the year 1885 Greenwich photographs are avail- 
able for measurement on 208 days, and photographs from 
India and the Mauritius, filling up the gaps in the series, 
on 152 days, making a total of 360 days out of 365 on 
which photographs have been measured. The record 
has thus been made practically complete for 1885 by 
means of the Indian and Mauritius photographs. 
A table of the means of daily areas of spots and facule 
and of th2 mean heliographic latitude of spots has been 
formed for each synodic rotation of the sun, and for each 
year from the commencement of the Greenwich series in 
1873 to the end of 1385. 
Further experiments for determination of the tempera- 
ture corrections for the horizontal and vertical force 
magnets by alternately warming and cooling the base- 
ment on sticcessive days were made in the spring of this 
year, a continuous record of the temperature being ob- 
tained by means of the Richard thermograph. The 
following are the results thus obtained in 1885 and 1886 
as compared with the previous determinations, the appa- 
