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