As the year 1761 was approaching, the scientific world was astir, pretty much as it is now. Halley’s computations were again gone over, and such corrections and improvements were introduced as the advance of astronomy since his day warranted and required. Governments gave their aid and supplied means liberally. One hundred and twenty positions had been carefully chosen, and the best results were confidently expected. The grand problem was about to receive a final and definite solution. The error in the ultimate result would certainly not exceed one‐fifth of one per cent. The astronomers were doomed to a sad disappointment. Wars then waging prevented some of the most important positions from being occupied by the observers. It was bitter for a well‐appointed party to sail for months and months over two oceans, only to see a hostile flag floating over the port they were about to enter. Sadly they sailed away, and could only see the transit from the rolling deck of their ship. Cloudy weather rendered other positions valueless. And even where everything seemed to promise success, an unforeseen phenomenon interfered to mar their work. The astronomer might have his best telescope duly mounted, and directed to the proper point of the heavens, and carefully adjusted; his eye might be glued to the instrument, as he watched on one side of his field of vision a portion of the circular edge of the sun’s disk, and on the other the round, black spot gradually approaching. As they drew near, his hand was raised to give the signal; his assistant stood ready to mark the very second when the two edges, coming nearer and nearer, would at last just touch. They hoped to seize the time of that first contact so accurately as to escape even the one second of error or doubt which Halley thought unavoidable. Vain hope! Before the contact, while Venus was still distant about two‐thirds of her own diameter from the edge of the sun, a dark streak or band seemed to interpose between them like a black cushion or wedge. As they pressed against it, the curved outlines of their edges seemed to be pressed back or flattened, as if by the resistance of the cushion, and to lose their normal shape. There was a pause in the onward movement, a quivering, a struggle, and then, by an irregular, convulsive jump, like that of two drops of water coalescing into one, Venus was seen to have already entered some way on the disk of the sun. The discomfited and astonished observer was forced to record that his uncertainty as to the precise time of the contact was not of one second only, but of at least twelve or fifteen seconds. Was it the defect of the instrument, or the fault of his own eye, over‐strained by long use, by the brilliant light, or by his intense anxiety? Or was there some unknown atmospheric cause at work producing this band? Anyhow, he might hope that other observers would be more fortunate than he had been. Again he was in error. Everywhere the same