The Past and Coming Transits and Arctic Explorations. 309 



to be 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. Ob- 

 servers 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 contact took place at ingress, and long 

 afterward at egress, so that the time to be noted was not that suddenly- 

 marked by the formation or breaking of a line ot 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 can not 

 be timed with sufficient accuracy to supi)ly evidence 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 circumstance, practically 

 rendering contact observations untrustworthy. We heard from the 

 head of the English party in Egypt, that, after internal contact 

 liad, 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 ac- 

 count 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 pre- 

 sented 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 ^un's limb, rendering the complete 

 cii-cle 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 to Avatch for. 

 The eye observations of contact, therefore, do not present results 

 of extreme value." Lieutenant Noble, at the same station, describes 

 the phenomenon as follows: "From about ten minutes of the time 



■> Thi« not only happens when Venus is placed as described, but when her disc is off the 

 Sdu's. Professor Norton, has seen the whole circuit of Venus surrounded by a border of light 

 at the time of inferior eoujiinction (within transii). In such case, the semi-circuiar arc of 

 light nearest the sun, coiisistg, in the main, of reflected sunlight, and the remaining are, in the 

 jtuain, ol refracted funligbt. 



