. 
Dec. 1, 1881} 
NATURE 
Itz 
to a Committee consisting of Sir George Airy, Prof. J. C. 
Adams, and Prof. Stokes. 
The Report of that Committee was forwarded to the India 
Office ; the following extracts from it contain those parts which 
refer to the main scientific questions raised :— 
“The object in referring these documents to the Royal Society 
was to assist the India Department in coming to a conclusion as 
to what, if anything, might yet be required in order to render 
the pendulum operations which have been carried out in connec- 
tion with the great trigonometrical suivey of India reasonably 
complete as an important contribution towards the determination 
of gravity all over the earth. 
‘© At present the stations which have been directly connected 
with the Indian stations are confined to Aden, Ismailia in Egypt, 
and Kew ; and no one of these has been differentially connected 
with any of the chains of stations that have hitherto been used in 
the determination in this way of the figure of the earth, though 
Kew is now a station at which an absolute determination has 
been made. We think it would be a reasonable expectation on 
the part of the scientific public that the Indian group of stations, 
which have already been connected with Kew, should be differ- 
entially connected with at least one chain of stations which are 
so connected with one another, and which have been employed 
in the determination of the figure of the earth. 
““We approve accordingly of the suggestion that gravity at 
Kew should be compared, by means of invariable pendulums, 
with gravity at another station belonging to another group. 
Greenwich has been named as such a station. 
“*In connection with this subject, we would refer to the 
suggestion, which has been brought before us, made by Mr. 
Peirce, of the United States Coast Survey, that Major Herschel 
should swing the same two pendulums that were used in India, 
first at Kew and then at Washington, 
‘© As Washington is, or shortly will be, connected differentially 
with a large chain of stations widely distributed in America and 
elsewhere, we think that the value of the Indian series would be 
decidedly incseased by being connected with one of the Ame- 
rican stations, such as Washington. We think, however, that 
its connection through Kew with one of the older series should 
not on that account be omitted. 
“« The observations required for the purpose of these connec- 
tions are such as certainly can be made, and have been made, 
by existing methods; and the labour of making them, which 
will be approximately in proportion to the number of stations 
at which the pendulums will have to be swung, is only a fraction 
of that already incurred on the Indian stations, and the three 
which have been included in the same group with them.” 
In October last a letter was received from the Treasury asking 
the opinion of the President and Council respecting arrange- 
ments for observing the transit of Venus in 1882, Under the 
advice of a Committee appointed for the purpose, it was recom- 
mended that a special Committee of the Royal Society should be 
appointed to decide upon the observations considered essential, 
and to advise Her Majesty’s Government as to the best method 
of carrying them out. In conformity with this advice, and at the 
request of the Treasury, a Committee was appointed to draw out 
a scheme of stations, and of the constitution, strength, and 
equipment of the observing parties, and to frame an estimate of 
the total cost. The Committee reported recommending the 
adoption of certain stations in South Africa, the West Indies, 
Australia, and New Zealand, and the Falkland Islands; and 
they at the same time added other particulars, and furnished an 
estimate of the whole, adopting in the main the recommenda- 
tions of that Committee; the Treasury then requested the 
President and Council to nominate an Executive Committee, 
by which (accounting to the Treasury) any vote of Parlia- 
ment for the purpose of these observations might be ad- 
ministered ; and under whose advice the observers and assistants 
might be selected and appointed. In compliance with this 
request the following Fellows were nominated as an Executive 
Committee, viz. the President, Prof. J. C. Adams, Sir G. Airy, 
Mr. Hind, Sir G. Richards, Prof. H. J. Smith, and Mr. Stone. 
That Committee is now continuing its labours, and has appointed 
its member, Mr. Stone, of the Radcliffe Observatory, Oxford, 
directing astronomer of the expeditions; and under him the 
selection of instruments, as well as the training of the observers, 
will be made. 
With a view of making the observations ultimately as com- 
parable as possible, the Committee, at an early stage, put itself, 
through the Foreign Office, into communication with the cor- 
responding Commissions in foreign countries, on the subjects of 
the instructions to be given to the various observers ; and a draft 
set of instructions, drawn up for this purpose, was circulated for 
comment and sugzestion, 
Moved perhaps in some degree by this action, the Governme n 
of France took advantage of the assemblage of scientific men 
collected in Paris for the Electrical Congress and Exhibition, to 
summon a Congress of Astronomers, having especially in view a 
consensus of arrangements for the ubservation of the Transit, 
This Congress met in Paris on October 5, under the auspices of 
the Minister of Public Instruction. M. Dumas was appointed 
President ; MM. Foerster and Weisse, Vice-Presidents; MM. 
Tisserand and Hirsch, Secretaries. The various countries of 
Europe were represented; but it was a matter of much regret 
that no representative from the United States of America was 
present. Mr. Stone attended on behalf of the British Com- 
mittee, I must here express my regret at having been unable to 
attend in person to support our directing astronomer, who made 
the journey at much inconvenience to himself ; but I should at 
the same time add that my absence in no way diminished the 
effectiveness of Mr. Stone’s counsels, which proved of great 
service in promoting a unanimity in the views finally adopted by 
the Congress. 
Two Committees were appointed: (1) for the selection of 
stations ; (2) for a discussion of methods of observation. 
As the British stations had been already chosen, and did not 
admit of material alteration, the first of these Committees did 
not directly concern us. But, judging from the number of 
observations contemplated to be made in South America by 
foreign expeditions, it seems not impossible that the party which 
we had proposed for the Falkland Islands might be advan- 
tageously transferred to some other locality, so as to strengthen 
the parties requiring support, for example, in Australia. 
As regards the discussion of methods, the draft instructions 
drawn up by the British Committee, and especially the definition 
of contact to be observed, strongly insisted upon by Mr. Stone, 
were in the main adopted. The following are the principal 
points agreed upon :— 
With a view to uniformity of method of observation it is 
necessary that instruments of nearly the same aperture (six inches) 
should be used, also that the observations of contact should be 
made in a field of just sufficient brightness to allow of the clear 
separation of two threads at one second of arc apart when seen 
projected on the sun with a power of 150. ‘The times corre- 
sponding to the internal contacts should be defined as follows :— 
At Ingress. —‘* The time of the last appearance of any well- 
marked and persistent discontinuity in the illumination of the 
apparent limb of the sun near the point of contact.” 
At Egress.—‘‘ The time corresponding to the first appearance 
of any well-marked and persistent discontinuity in the illumina- 
tion of the apparent limb of the sun near the point of contact.” 
It is a point of primary importance that all the observers shall, 
as far as possible, observe the same kind of contact; and it is 
therefore desirable that the times recorded for contacts should 
refer to some marked adzscontinuity in the illumination of the 
sun’s limb about which there cannot be a doubt, and which may 
be supposed to be recognisable by all the observers. If a pure 
geometrical contact is alone seen, there can be no doubt about 
the time which should be given; but, if haze is noted, it should 
be haze nearly as dark as the cuter edge of the planet; and if a 
ligament is seen, it should be nearly as dark as the outer edge of 
the planet. 
A further proposal was made to establish a Central Bureau in 
Paris to receive and discuss the observations, and to enter upon 
other work more or less directly connected with the determina- 
tion of solar parallax. But, as this question was not contem- 
plated in the instructions given to our representative, and indeed 
exceeded the powers of the British Committee, no definitive 
resolution was passed on the subject. 
On the subject of the longitude of a point in Australia, to 
which I made allusion in my address last year, as important for 
the observations of the transit of Venus, I have lately received 
a letter from Mr. Todd, of the Observatory, Adelaide, from 
which the following is an extract : ‘‘ With regard to the deter- 
mination of Australian longitudes: as it is uaderstood that 
Lieut.-Commander Green, U.S.N., will call at Port Darwin to 
determine its longitude by signals from Singapore on the one 
side, and with the Adelaide Observatory on the other, I have 
taken no further steps for going to Port Darwin, as previously 
arranged, I shall take all the necessary observations here, and 
