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however, in the data, upon which his calculation was founded, he began to observe on the 23rd of November. His own account of bis observation, on Sunday the 24th of November, is this: “Observavi enim die 24 solis exortu ad horam usque nonani, item paulo ante decimam ipsoque demum meridie et horà 1 pomeridianâ (ad) 2: aliis temporibus ad majora avocatus quæ utique ob hæc parerga negligi non decuit.” “Venus in Sole Visa," published in Hevelius's, “Mercurius in Sole Visus," 1662 Folio.

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from 9 A. M. to a little past 10, and again from 2 till a little past 3, to go to church. On returning at 3h 15" P. M. he observed the planet just wholly entered upon the Sun's disk. He did not live to publish his observation. In a letter to his friend Crabtree dated Oct. 3, 1640, he states that he is about finishing the account; and in another letter dated Dec. 12, 1640," he says, “I have changed my 'Venus in Sole Visa' in some respects, but have cot yet leinure to transcribe it. And if that were done, I do not yet know how I shall contrive to publish it.”—In Dec. 19, 1640, he again writes, stating his intention of visiting his friend, on the 4th of the succeeding January, unless something very remarkable should happen. He died suddenly on the morning of the previous day, Jan. 3, 174;: as appears from the endorsement of his letters, by Crabtree.

NOTE F. (G.) LECTURE IV. p. 85.

On the transits of Venus, hitherto observed.

In a scientific point of view it is curious to notice the different circumstances, under which the transit of Venus was observed, in 1639, and in 1761, and 1769. Horrox and his friend Crabtree were the only two persons who

f Wallis. Horroccii Opera Posthuma, p. 337.
P“ Nisi quid præter solitum evenerit.”

observed the first. Previously to the transit in 1761, Halley had directed the notice of Astronomers to the importance of the observation for determining the Sun's horizontal parallax. And Joseph Delisle published a work upon the subject. Several months before the transit happened, Maskelyne was sent from England to St. Helena, and Mason sailed for Sumatra, Le Gentil went to India, Chappe to Siberia, Perigrè to the island Rodrigue in the Indian Ocean. Observers were also sent into Lapland and Norway, and by the Academy of Petersburg to the borders of Tartary and China. Observations were made, with different degrees of success, in Siberia, at the Cape of Good Hope, in the Indian Sea, at Madras, at Trinquebar, at Pekin, and at St. John's, Newfoundland. Still more extensive preparations were made for observing the transit in 1769. From England observers were sent into North America, to the islands of the South Sea, and to Madras. From France observers set out for California, St. Domingo, and the East Indies. From Russia, into three different places of Russian Lapland, and into Asiatic Russia, the borders of the Caspian Sea, and other places. (See Mem. of Acad. of Petersburg, Vol. xiv.) The king of Denmark sent to Wardhuys, nearly the most northern extremity of Europe ; and Planman observed at Cajanebourg in Finland. (See Montucla Histoire des Mathematiques, Part IV. Liv. v. § 11. Vol. iv. pp. 102, 112. Mém. de l'Acad. 1771, 1772, 1781.

Mém. de Petersbourg, 1769.)

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