Prof. Winthrop Gets a Good Look at Venus

Prof. John Winthrop of Harvard College (portrayed here by John Singleton Copley, in an image that comes courtesy of the university’s Collection of Historical Scientific Instruments) was among the many scientists who scrambled to observe the transit of Venus in 1761.

His report on the event to the worldwide scientific community included praise for “His Excellency FRANCIS BERNARD, Esq. Governor of the Province of the Massachusetts-Bay, inspired with a just zeal for the advancement of Literature, which he demonstrates on every opportunity.”

In 1761 Bernard was newly arrived in Massachusetts, and that April he helped secure government support for Winthrop’s research. In just a few years the governor would become very unpopular, with Winthrop quietly supporting that Whig opposition.

As the professor knew from Edmund Halley’s calculation years before, “Newfoundland was the only British Plantation in which one [observation] could be made, and indeed the most western part of the Earth where the end of the Transit could be observ’d.” Therefore, he set out for “the Savage coast of Labrador” with two recent Harvard graduates, Samuel Williams and Isaac Rand, both eighteen years old. They took along most of the college’s astronomical equipment, viz.:

an excellent Pendulum clock, one of Hadley’s Octants with Nonius divisions and fitted in a new manner to observe on shore as well as sea, a refracting telescope with cross wires at half right angles for taking differences of Right Ascension and Declination, and a curious reflecting telescope, adjusted with spirit-levels at right angles to each other and having horizontal and vertical wires for taking correpondent altitudes, or differences of altitudes and azimuths.

Winthrop and his assistants arrived in Newfoundland on Massachusetts’s provincial ship in late May 1761. They set up their equipment and checked and rechecked it, Winthrop wrote, “with an assiduity which the infinite swarms of insects, that were in possession of the hill, were not able to abate, tho’ they persecuted us severely and without intermission, both by day and by night, with their venomous stings.”

The morning of 6 June was “serene and calm.” Prof. Winthrop wrote:

at 4h 18m we had the high satisfaction of seeing that most agreeable Sight, VENUS ON THE SUN, and of showing it in our telescopes to the Gentlemen of the place who had assembled very early on the hill to behold so curious a spectacle. The Planet at first appear’d dim thro’ the cloud, but in a short time became more distinct and better defined.

Winthrop recorded the time of transit and sketched what he saw, telling his readers:

The above observations gave me so many differences between the Sun’s and Venus’s altitudes and azimuths, from whence by spherical trigonometry I deduc’d the Planet’s right Ascensions and Declinations and, from them, in the last place, her Longitudes and Latitudes. It would be neither of entertainment nor use to the Reader to insert the particulars of such tedious calculations. . . .

The comparison of the observations made in the N.W. parts of the world with those in the S.E., when all of them come to be laid together, will give the true path of Venus, abstracted from parallax, by which means the quantity of the parallax will at length be discovered. The right determination of which point will render this year 1761 an ever-memorable era in the annals of astronomy.

Those quotations comes from this edited version [P.D.F. download] of Winthrop’s report.

Winthrop planned to view the 1769 transit from Newfoundland as well, but a fire at Harvard destroyed the astronomical instruments. He asked Benjamin Franklin to send a new set from London, as this Dutch Transit of Venus website describes.

Unfortunately, there was a heavy demand for astronomical devices all over Europe as the second transit approached. Then telescope-maker James Short died before delivering Winthrop’s order. On 11 March 1769, Franklin wrote to Winthrop that he’d managed to get that brass reflecting telescope from Short’s estate, but he was still waiting for the other tools from another craftsman. During the 1769 transit, Winthrop was stuck in Cambridge.

(Thanks to Boston 1775 reader Robert C. Mitchell for some of the links used in this posting.)