178 
which arise from the use of all such measuring instru- 
ments, use the sun itself as our circle of reference, and 
infer the displacements by observing the differences in 
time at which Venus is apparently in contact with the 
sun’s limb, as seen from the opposing stations. The last 
method is that upon which reliance has been chiefly 
placed in the organisation of the British expedition. For 
the success of this method, we have to place observers at 
two sets of opposed stations, at one of which Venus is 
thrown, from the effects of perspective, towards the centre 
of the sun at ingress, whilst at the other set of stations 
Venus is thrown from the effects of perspective from the 
centre. The former stations are called stations of accele- 
rated ingress, the latter those of retarded ingress. 
The stations of the egress observations are chosen 
from similar considerations, and divide themselves into 
stations of accelerated egress and retarded egress. In 
the selection of stations, the most important points are, 
that the effects of the apparent displacements on the dif- 
ference in the times of contact should be considerable, 
that the climatic conditions should be generally favour- 
able, and that the altitude of the sun should be sufficient 
to render a good observation possible. 
The principal stations selected for the British observa- 
tions of accelerated ingress were Madagascar and the 
Cape; but it is hoped that good observations may have 
been secured by Mr. Meldrum, the director of the 
observatory at Mauritius, although the altitude of the sun 
is very low for that station at the time of contact. The 
observers at Madagascar were the Rev. S. J. Perry and 
the Rev. W. Sidgreaves, with Mr. Carlisle as an assistant. 
The instruments provided were excellent 6-inch equa- 
torials. The expedition was placed under the care of 
Commander Aldrich, of H.M.S. Fawz, with instructions 
to establish the observers near the coast on the south- 
western part of the island. A telegram has been received, 
stating that the Fawn had returned to Natal, and that 
the observations had been perfectly successful. 
The observations at the Cape have also been successful. 
At the Observatory there, Mr. Gill reports that seven 
observations of contact were made. The instruments 
available at this station were a fine 7-inch telescope by 
Merz, which belongs to the Observatory, and a new 6-inch | 
equatorial by Grubb, sent out by the Committee for the 
observation of the transit, and a good Dollond, which 
was used at the last transit, with an aperture of nearly 
four inches, and Mr. Gill’s heliometer. The goodness of 
the contact observations with the latter instrument may 
be open to doubt, from the construction of the instrument 
with a Civided object-glass. Three of the contacts must, 
I fear, have been made with inferior instruments, but at 
least three good observations of contacts have been made 
at this station alone. 
Mr. Marth, who is in charge of the station at Montagu 
Road, on the railway between Cape Town and Beaufort 
West, reports that two good observations of contact have 
been secured. The observers at this station were Mr. 
Marth and Mr. C. M. Stevens, with Corporal Thornton 
as assistant. The instruments provided were a 6-inch 
equatorial by Grubb and the fine Dallmeyer instrument 
which was kindly lent by Dr. Warren de la Rue for the 
observation of the transit. 
At Aberdeen Road, Mr. Finlay, B.A., First Assistant 
at the Cape Observatory, and Mr. Pett, Third Assistant, 
were the observers. The instruments were 6-inch 
equatorials by Simms, provided by the Committee; a 
marine artilleryman, Gunner Shean, was sent out from 
England with the instruments, and was attached to the 
party as an assistant. The observations have been 
perfectly successful, and the definition is reported to 
have been fine. 
Mr. Neison has also observed the contacts at Durban, 
Natal, with a fine equatorial provided by the liberality of 
the colonists for the observations. Therefore we have at 
NATURE 
[ Dec. 21, 188 
least ten first-rate observations of the internal contact at 
the phase accelerated ingress made upon one uniform 
plan and with instruments of the same class. 
The longitudes of all the Cape stations have been 
directly connected with that of the Cape Observatory by 
telegraph, and the longitude of that station has recently 
been connected by telegraphic determination with Green- 
wich. ? 
The Greenwich times of the phase of accelerated in- 
gress range from about 2h. 11m. os. for Madagascar to 
2h, 12m. 8s. for the Cape Observatory. The Greenwich 
mean time for the general body of observations known to 
have been secured would not differ greatly from 2h. 
11m. 48s. 
But the observations made of this phase would have 
been perfectly useless unless observations for compari- 
son with them had been made at stations of retarded 
ingress. 
The stations selected for the observation of retarded 
ingress were Jamaica, Barbadoes, and Bermuda. But 
the Canadian Government also provided three 6-inch 
telescopes; and one of their observers, Lieut. Gordon, 
Director of the Observatory at Toronto, came over to 
England to secure the necessary additions to the instru- 
mental means, and to Oxford to make himself acquainted 
with the arrangements of the other British stations. It 
is to be feared that this spirited conduct on the part of 
the Canadian Government has not been followed by the 
success which could have been wishe1; but no official 
reports have yet been received from the Canadian 
stations. 
The phase of retarded ingress has been successfully 
observed by all the observers sent out in the British ex- 
peditions, and the observations, from the telegrams 
received, appear to have been perfectly satisfactory. 
The observers at Jamaica were Dr. Copeland and Capt. 
Mackinlay, k.A. Mr. Hall was to have observed the 
contact at another part of the island away from telegra- 
phic communication, and he has not yet reported. 
The observers at Bermuda were Mr. Plummer, Lieut. 
Neate, R.N., and Capt. Washington, R.E. 
The observers at Barbadoes were Mr. Talmage and 
Lieut. Thomson, R.A. 
We have therefore, at these stations alone, seven good 
observations of retarded ingress. 
The Greenwich times of the phase of retarded ingress 
range from about 2h. 22m. 35s. at Barbadoes, to 2h. 24m. 
25s. at Bermuda. The Greenwich mean time for all the 
observations will not differ greatly from 2h. 23m. 33s., 
and the available difference between the opposed stations 
of accelerated and retarded ingress will therefore be 
about 7oos., and an error of five seconds in the determi- 
nation of the difference of the observers would not give 
rise to an error of 700,000 miles in the determination of 
the sun’s distance, because 5 seconds is only the 140th 
part of the available interval. But even if the separate 
results at a station should occasionally disagree, 10 
seconds of time zw/er se there is no reason whatever why 
the mean difference in time between the opposed stations 
derived from seven good contacts at one end, and ten at 
the other, should have an error of three seconds of time. 
So that from the British observations of ingress alone it 
should be possible to estimate the sun’s distance within 
300,000 miles. 
The stations at Bermuda, Jamaica, and Barbadoes, 
which served for retarded ingress, are also available for 
accelerated egress. 
The egress observations at Jamaica and Barbadoes 
are reported as satisfactory. Those at Bermuda were 
apparently only picked up through clouds. It is possible, 
therefore, that the Bermuda observations may not be 
available, on this account, for combination with the other 
observations ; but with the Jamaica and Barbadoes 
observations alone we have at least four good contacts. 
