( 121 ) 



The longitude of our station now being determined as well as 

 possible, I shall proceed to communicate our contact observations of 

 Venus and the Sun during the Transit on December 9'''. 



Our place of observation was on the battery, in the immediate 

 neighbourhood of the pavilion of the heliometer ; its longitude must 

 therefore be accepted to be 3''41'"47%81 + ü^26 --. 3''41"^48^07. 



The ingress took place very early in the morning, the sun being- 

 only live degrees above the horizoJi. unfortunately at sunrise the 

 sky was not quite clear. In the east, a few degrees above the horizon 

 there was a dark stratus, and it was to be feared that at the instant 

 of the second contact the sun would just be behind it. So it happened, 

 and this was the more unfortunate as the station Reunion had 

 expressly been chosen for the observation of that contact. 



At the first contact the sun's limb was very unsteady. At 5''38'"20^ 

 mean time St. Denis, I thought that 1 saw an impression on the 

 sun's limb, which I held to be made by Venus. A passing cloud, 

 however, prevented me from seeing whether I had been right. 

 When, after a minute the sun reappeared, I could not distinguish 

 the impression on the limb any more. At 5''41"'20s it could however 

 be seen plainly. The place where I then saw it was exactly the 

 same as that where I had thought to see it 3 minutes earlier. However, 

 as Venus had moved on 6" during those 3 minutes, the observation 

 of the tirst contact must be considered as having failed. The mean 

 between the two instants mentioned is no more than a very rough 

 approximation. 



As said already, the second contact was missed. 



But both Mr. Sop:ters and I observed the two last contacts. 



The formulae, given in the Nautical Almanac of 1874 on p. 434 

 for the calculation of the contacts, are: 



For the iirst external contact : 

 / = 13'^45™58s — [2,5773] q sin /— [2,7049] q cos I cos (A + 136°39'.9), 



for the first internal contact : 



j^=zl4hl5'"2#— [2,6992] q sin l— [2,7462] q cos I cos {X + 147°55'.7), 



for the second internal contact : 



t = 1 7i'57™26s + [2,8253 ] q sin I + [2.5265] q cos I cos (X — 55°37'.8), 



for the second external contact : 



^=18i'26m54^ + [2,7374] q sinl-}- [2,5014] q cos I cos (X — 37°50'9); 



The times are given in Greenwich mean time; and q stands for 

 the radius, / for the geocentric latitude and X for the longitude east 

 of Greenwich of the place of observation. 



