https://en.wikipedia.org/wiki/File:Observatoire_de_Peking.jpg
I was doing some research for a novel, and I came across this image. To the left in this illustration, unconnected to the rest of the astronomical tools, is what appears to be a hole in the ground. I don't see the hole (if that's even what it is) in any of the photos of the Observatory that turned up in a google image search. Can anyone tell me what it was for? I should note that this isn't the only European illustration that features this... whatever it is.
(Really hoping it isn't a toilet.)
Hmm, yes it seems there's at least three 18th-century European copper engravings like that. (another is this one), but they're so similar (except being mirrored) that it seems likely one must be copying another, or that they were prepared from some common source, such as a sketch. (which would be expected, it's pretty unlikely any of the engravers went to China and saw it with their own eyes) Also, it wasn't uncommon that they either misinterpreted, or embellished things (I've got a print where they invented a building out of nothing just to balance the picture). So just because it was there in multiple contemporary pictures still doesn't mean it necessarily existed.
Although I suppose the question still stands even if it didn't exist, since whoever invented it then must've had some idea of what he was drawing.
Could be related to Eratosthenes's method for calculating the size of the earth. Makes me wonder whether the Chinese were familiar with that method, or the Jesuits added that hole when they helped update the observatory.
