176 PHILOSOPHICAL TRANSACTIONS. [aNNO 1771. 



2. Transit of Venus by Capt. Cook, with a reflecting telescope of 2 feet 

 focus, and the magnifying power 140. 



June 2, < 



The first visible appearance of $ on the 0's limb, see fig. 1. ... 21 25 45 

 First internal contact, or the limb of $ seemed to coincide with 



the 0's, fig. 2 21 43 15 



A small thread of light seen below the penumbra, fig. 3 21 44 15 



Second internal contact of the penumbra, or the thread of light June 3, 



wholly broke 3 14 13 



Second internal contact of the bodies, and appeared as in the first 3 14 45 



Second external contact of the bodies 3 31 22 



Total egress of penumbra, dubious 3 32 2 



The first appearance of Venus on the sun, was certainly only the penumbra, 

 and the contact of the limbs did not happen till several seconds after, and then 

 it appeared as in fig. the 4th ; this appearance was observed both by Mr. Green 

 and me; but the time it happened was not noted by either of usj it appeared 

 to be very difficult to judge precisely of the times that the internal contacts of 

 the body of Venus happened, by reason of the darkness of the penumbra at 

 the sun's limb, it being there nearly, if not quite, as dark as the planet. At 

 this time a faint light, much weaker than the rest of the penumbra, appeared 

 to converge towards the point of contact, but did not quite reach it, see fig. 2. 

 This was seen by myself and the two other observers, and was of great assist- 

 ance to us in judging of the time of the internal contacts of the dark body of 

 Venus, with the sun's limb. Fig. the 6th is a representation of the appearance 

 of Venus at the middle of the egress and ingress, for the very same phenomenon 

 was observed at both: at the total ingress, the thread of light made its appear- 

 ance with an uncertainty of several seconds; 1 judged that the penumbra was in 

 contact with the sun's limb 10^ sooner than the time set down above; in like 

 manner at the egress the thread of light was not broke off or diminished at once, 

 but gradually, with the same uncertainty; the. time noted was when the thread 

 of light was wholly broke by the penumbra. At the total egress I found it dif- 

 ficult to distinguish Venus's limb from the penumbra, whi h of course made the 

 second external contact a little doubtful, and the precise time that the penumbra 

 left the sun could not be observed to any great degree of certainty, at least by me. 

 Some of the other gentlemen, who were sent to obser\'e at diflferent places, saw 

 at the ingress and egress the same phenomenon as we did; though much less 

 distinct, which no doubt was owing to their telescopes being of a less magnify- 

 ing power; for the penumbra was visible through my telescope during the whole 

 transit; and Dr. Solander, whose telescope magnified more than ours, saw it, I 

 have reason to think, distincter than either Mr. Green or myself; though we 

 both of us saw enough to convince our senses, that such a phenomenon did in- 



