Astronomy explained upon Sir Isaac Newton's principles. And made easy to those who have not studied mathematics / To which are added, a plain method of finding the distances of all the planets from the sun, by the transit of Venus over the sun's disc, in the year 1761. An account of Mr. Horrox's observation of the transit of Venus in the year 1639; and, of the distances of all the planets from the sun, as deduced from observations of the transit in the year 1761. By James Ferguson.

James Ferguson

Date:: 1770

Credit: Astronomy explained upon Sir Isaac Newton's principles. And made easy to those who have not studied mathematics / To which are added, a plain method of finding the distances of all the planets from the sun, by the transit of Venus over the sun's disc, in the year 1761. An account of Mr. Horrox's observation of the transit of Venus in the year 1639; and, of the distances of all the planets from the sun, as deduced from observations of the transit in the year 1761. By James Ferguson. Source: Wellcome Collection.

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the beginning of egrefs as feen from the Earth’s center, in order to have the true time of total in- erefs and beginning of egrefs as feen from places in the hemifphere YHO: and juft the reverfe for places in the hemifphere V [O.—It was proper to mention thefe circumftances, for the reader’s more eafily conceiving the reafon of applying the times anfwering to the parallaxes of longitude and latitude in the fubfequent part of this article : for it is their fum in fome cafes, and their difference in others, | which being applied to the times of total ingrefs and beginning of egrefs as feen from the Earth’s center, that will give the times thereof as feen from the given places on the Earth’s furface. | 52. The angle which the Sun’s femidiameter fabtends, as feen from the Earth, at all times of the year, has been fo well afcertained by late ob- latitude has alfo been fo well afcertained at many different times of late, that we have very good reafon to believe it will be 9° 43” fouth of the Sun’s center, at the time of her conjunétion with the Sun.—If then, her femidiameter at that time be 37° 2 (as mentioned by Dr. Hatiey) it appears by the projection (Fig. 2.) that her total ingreis on the Sun as feen from the Earth’s center, will be at 28 minutes after I] in the morning (§ 40.) and her beginning of egrefs from the Sun will be 20 minutes after VIII, according to the time reckoned © at London. | £3. As the total ingrefs will not be vifible at London, we fhall not here trouble the reader about Venus’s parallax at that time.—But by projecting the fituation of London on the Earths difc (Fig. 4.) for the time when the eerefs begins, we find it will then be at /, as feen from the Sun. | ee Draw /d parallel to Venus’s orbit VCO, and /# perpendicular to it: the former is Venus’s eaftern parallax in longitude at her beginning of egtefs, : and

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