268 
POPULAR SCIENCE REVIEW. 
Venus, outside the sun, a ring which is not to he regarded as 
mere sunlight, but as a distorted image of the sun himself.* 
The effect of this phenomenon in modifying the conditions 
under which internal contact is observed will be recognised at 
once. Observers were told to look for the moment when a line 
of sunlight suddenly made its way between the disc of Venus 
and the solar limb at ingress, or when the gradually narrowing 
line of sunlight was suddenly broken at egress. But here was 
true sunlight bounding the disc of Venus long before true con- 
tact took place at ingress, and long afterwards at egress, so 
that the time to be noted was not that suddenly marked by the 
formation or breaking of a line of sunlight, but that when the 
sunlight, bounding the part of Venus outside the solar disc, was 
seen at ingress to become merged in the true outline of the sun, 
or at egress just began to disturb that outline. The observation 
to be made was of precisely the same order as an observation of 
external contact, and it had long been admitted that external 
contact cannot be timed with sufficient accuracy to supply 
evidence available for determining the solar parallax. 
The very first news which reached us on the morning of 
December 9 pointed to this difficulty, or rather to this circum- 
stance practically rendering contact observations untrustworthy. 
We heard from the head of the English party in Egypt that, 
after internal contact had in reality been established at egress, 
an arc of sunlight still remained visible around the part of 
Venus which was outside the sun ; and that the observer, 
through waiting for this arc to break, lost the best cusp- 
measurements. Captain Tupman gives the following account 
of the phenomenon as observed at the stations where the 
transit began earliest of all, viz. the set of stations on the 
Sandwich Isles: — “The important phase of the phenomenon 
of internal contact presented wholly unexpected appearances, 
totally unlike what we had been led to anticipate. For 
many minutes before contact a faint light was seen behind 
Venus, beyond the sun’s limb, rendering the complete circle of 
her disc visible. From that time until the establishment of 
complete contact no sudden or definite phase could be seized 
upon, such as the practice with the working model induced us 
* This not only happens when Venus is placed as described, but when her 
whole disc is off the sun’s. Professor Norton has seen the whole circuit of 
Venus surrounded by a border of light at the time of inferior conjunction 
(within transit). In such a case the semicircular arc of light nearest the 
sun consists, in the main, of reflected sunlight, and the remaining arc, in the 
main, of refracted sunlight. 
