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I don't think I've got a definitive answer on that. In my mind, based on modern derailleurs, I'd automatically set it up the way show in your picture. However [1], it has been pointed out to me by a number of old timers that it should be the way @falconvitesse has it. If you refer back to the sales adverts where they are pictured, it's common to see them that way round. However [2], it's also worth bearing in mind that those pictures are often embellished with artist's impressions, it could have been drawn by someone who doesn't know bikes, plus you can't guarantee the builder put it on correctly for the picture either. To confuse things further, they seem to work either way round, so there's always a chance it should be how you've got it!
Jonny69-
Falconvitesse's Simplex is a Juy 51, the mech in The.Gren's pic is a Tour de France, incidentally with the jockey cage upside down.
The difference ( so far as I can see) is that, apart from the second cable, the Juy 51 has the end of the plunger shaft connected to the middle of the jockey cage, whereas with the TdF the shaft is connected to the bottom of the cage and supports the bottom jockey wheel.
The nut on the end of this shaft holds everything together and is difficult to tighten. I covered mine with a blob of araldite. It hasn't fallen off, yet.
How's that for escapism on a dark day?
P.S. Jonny 69 is correct, they can work ok upside down, but M. Juy intended the TdF to be used as I have described.
clubman
I'm pretty sure your cage needs to go through a 180 - the jockey in line with the coil spring should be at ze top - non ?