The Transit of Venus provided the first accurate value for the Sun's parallax which enables one to determine its distance. Edmond Halley proposed the method in a 1716 paper published in Philosophical Transactions, Vol. XXIX, No. 348, p. 454 and is written in Latin. There is an abridged English translation available at Google Books and a .pdf version online which includes a better view of the figure.
Supplemental (Jun 19): For an account of the observations see Newcomb, Popular Astronomy, p. 177.