The Transit of Venus in Philadelphia 1769

An illustration from the first volume of the Transactions of the American Philosophical Society, showing the path of the Transit of Venus as observed in Philadelphia in 1769.

One of the disad-vantages of having a quarter of a million books for sale is that sometimes it is easy to forget what you have, even with a database to help you. This morning Ken [BTC’s cataloguer Ken Giese, who works on archives and pre-20th Century material for us] walked into my office and said, “So, this Transit of Venus…” Having just had my first jolt of caffeine, and having spent the weekend trying to get at least one of my children the least bit excited about witnessing a celestial event that will not occur again in their lifetimes, I immediately jumped in, “Corey [BTC’s photographer, Corey Bechelli, with whom I share an office] and I were just talking about it. We might go up to the roof around 6pm. We figure we’ll have an excellent view from there and I brought in binoculars to make one of those safe viewing thingies [caffeine apparently not doing much for my vocabulary of astronomical instruments just yet].” (BTC’s flat-top roof was featured in a previous blog post)

Ken, having graciously allowed me to interrupt him, continued, “Well, there’s an interesting Philadelphia connection to the Transit of Venus.” Again I cut him off, “Right. David Rittenhouse, the colonial-era Philadelphia clockmaker and a very early American astronomer, made important observations of the Transit of Venus. It was the key to determining the earth’s distance from the sun.”

Cart of Volumes Awaiting Photography, Including Rittenhouse's Paper on the Transit of Venus

While Corey and I discussed the Transit of Venus, unbeknownst to us an original printing of Rittenhouse’s paper on the subject was sitting on a cart right between our desks.

Pausing for a moment to reflect how rude I’d been, I asked Ken, “I’m sorry, what were you going to say about the Transit of Venus.” He pointed right behind me, to a cart of bound periodicals waiting to be photographed by Corey, and said, “Well, coincidentally, that set of the Transactions of the American Philosophical Society prints David Rittenhouse’s paper on the 1769 Transit.”

Maybe I should shut up and turn around more often.

(Ken’s description of the periodical set containing Rittenhouse’s paper on the Transit of Venus can be found on our website at

– Dan Gregory