Fune 8, 1871 | 
NATURE 
103 

ANNUAL VISITATION OF THE ROYAL 
OBSERVATORY 
N Saturday last the Board of Visitors of the Royal 
Observatory made their annual visitation to our 
National Observatory to examine into the work done, and 
to receive the Report of the Astronomer Royal. We have 
not space for the report in full, but this is not to be re- 
gretted, for it contains a quantity of minute detail about 
trivial matters which the ordinary run of mankind would 
not think worth the printing. 
There are, however, several points of great scientific 
interest in the Report, the new Water Telescope and the 
instruments for use in the approaching observations of 
the Transit of Venus having been the lions at Greenwich. 
The correction for level-error in the transit instrument 
having become inconveniently large, owing apparently to 
a gradual subsidence of the eastern support since the 
erection of the instrument, about a ton weight of stone 
was placed on the western pier. Not the slightest change, 
however, could be traced as due to this; the level-error 
maintaining its usual value. This plan having failed, the 
stones were removed, and a sheet of very thin paper, 
stp inch in thickness, was placed under the eastern Y, 
which was raised from its bed for the purpose. The col- 
limators having been observed just before this operation, 
no difficulty was experienced in adjusting the instrument so 
as to have very nearly the same error of Azimuth as before. 
The mean annual value of the level-error appears to be 
now sensibly zero. This will give some idea of the deli- 
cate arrangements necessary for this ponderous instru- 
ment. 
The usual course of Astronomical observations now 
carried out for so many years has been adhered to. The 
list of fundamental stars used for determination of clock- 
error has been increased to 210. Besides these, Nautical 
Almanac, circumpolar, and moon-culminating stars have 
been observed ; also refraction stars, stars with large 
proper-motion, and stars which are required for any special 
investigation. A few of Bradley’s stars which had been 
inadvertently omitted have been observed in the past 
year. The Sun, Moon, and large planets have been ob- 
served as usual. As the siege and war operations in 
Paris seriously interfered with the observations of small 
planets made at the Paris Observatory, observations of 
them were continued at Greenwich throughout each entire 
lunation during the investment of the city. 
The observations of y Draconis, the star which passes 
very near the Zenith of Greenwich, with the Water 
Telescope, made in the spring of the present year, are 
completely reduced, with the exception of a small correc- 
tion for the positions of the micrometer-wires, to be 
determined shortly. As the astronomical latitude of the 
place of observation is not known (it is not many yards 
from the transit circle), the bearing of these observations 
on the question of aberration cannot be certainly pro- 
nounced until the autumn observations shall have been 
made ; but, supposing the geodetic latitude to be ac- 
cordant with the astronomical latitude, the result for 
aberration appears to be sensibly the same as with 
ordinary telescopes. 
With regard to the Magnetic instruments, the Astro- 
nomer Royal states that a plan was arranged last year 
for photographic impression of hour-lines upon the photo- 
graphic sheets carrying the records of the three Magnet- 
ometers and of the Earth-current Galvanometers: an 
arrangement already for some time carried out in the new 
instruments by Dr. Balfour Stewart. The beam of light, 
constantly directed through a cylindrical lens to fall upon 
the sheet, emanates from one of the existing lamps, or (in 
one instrument), from a flame specially mounted for it ; it 
is, however, obstructed by a shade till 25 minutes before 

connections of the shades were so arranged that all could 
be opened and closed by a single wire. 
The following numerical results of the magnetic 
elements for 1870 may be interesting :— 
Mean westerly declination 19° 54’ nearly. 
§ 3°865 (in English units). 
) 
Mean horizontal force. . . 1 1°782 (in Metrical units 
Md. eo 
6751 9 (by 9-inch needles). 
Meanidipiet< ierbe o 67 52 25 (by 6-inch needles). 
67 53 41 (by 3-inch needles). 
The observations of dip at different hours appear to 
show a diminution from gh. A.M. to 3h. P.M. 
A small Appendix of great interest is attached to the 
report. Those who have given attention to the history of 
Terrestrial Magnetism are aware that Halley’s Magnetic 
Chart is very frequently cited ; but the Astronomer Royal 
could not learn that any person, at least in modern times, 
had ever seenit. Inquiries were made of nearly all the 
principal scientific bodies in Europe, and in several of 
the best continental libraries in vain. At last, by the 
assistance of Mr. Winter Jones, Principal Librarian of 
the British Museum, a copy was discovered in the library 
of the Museum. 600 copies have been taken ina reduced 
size, for insertion, as an Appendix, in the Magnetical and 
Meteorological volume for 1869. 
On the subject of Chronometers it is remarked, “ The 
performance of chronometers, as depending on their 
mechanical construction, is very admirable; I have re- 
marked but one point on which I could desire change, 
namely, that the balance should be struck more lightly, at 
a greater distance from its axis; the late Mr. Charles 
Frodsham, at my suggestion, had made experiments on 
this point, which promised to be successful. The princi- 
pal errors of even moderately good chronometers are, 
however, produced by defective compensation, which the 
most skilful makers cannot perfectly manage. I have long 
been of opinion that the final adjustment for compensation 
ought to be made by some more delicate operation than 
that which suffices for approximate compensation ; but 
the able chronometer-makers whom I have consulted 
have not yet devised a satisfactory plan.” 
With reference to Time Signals, we read that a proposal 
has been made to have a time-ball dropped at Queens- 
town, and that the report of the Westminster Clock shows 
that 55 per cent. of its errors are under 1, and 94 per cent. 
under 3°. 
In December two attempts were made to determine the 
longitude of Gibraltar, at the request of Professor New- 
comb, but without success, the cable connecting Falmouth 
and Gibraltar being out of order. 
During the year the time of the Astronomer Royal has 
been partly occupied in preparations for the Transit of 
Venus, 1874. Measures have been taken for equipping each 
of five stations witha Transit, an Altazimuth, and an Equa- 
toreal. Some other instruments mounted in temporary 
observatories were inspected by the visitors. Of Transits 
there are five new, all mounted on stone piers. Of clocks 
to accompany them, there are two from the Royal Obser- 
vatory, three new. Of Altazimuths, one from the Royal 
Observatory, four new. Of Equatoreals, 6 inches in 
aperture, and carried by clock-work, there are five, pur- 
chased or new. Of clocks of an inferior class, to accom- 
pany the two last classes of instruments, one can be 
supplied, nine must be procured. Fifteen portable obser- 
vatories must be prepared, of which specimens were 
exhibited to the visitors. The Royal Observatory can 
supply three 4-inch detached telescopes, and two more 
will be desirable. 
The report goes on to say :—“My preparations 
have respect only to eye-observation of contact of 
limbs. With all the liabilities and defects to which 
it is subject, this method possesses the inestimable 
each hour, and acts till 24 minutes after each hour. The | advantage of placing no reliance on instrumental 
