the first transit in 1631

Recently heard about Pierre Gassendi, a French philosopher, priest, scientist, astronomer, and mathematician, who published the first data on the transit of Mercury in 1631. He was the first to observe it, using Kepler's calculations.

I tried to figure out how he did that exactly... Telescopes would have been fairly new then. And accurate clocks were not around. I considered filtering too. Surely, he did not directly, visually, through the telescope, with his eyes, observe the event. Hopefully, he did not blind himself. He must have used projection. I did a bit of research and learned that is, in fact, what he did.

He also explained parhelia in 1629 as due to ice crystals. Among other astronomical phenomena. Interesting guy.