This Idéal derailleur is pleasingly elegant. In the style of the times it is a sliding rod mechanism, but its genius is that the sliding rod slopes down at an angle, to allow the derailleur to follow the profile of the freewheel. In this way it maintains a relatively constant chain gap - prefiguring SunTour's 1960s slant parallelogram that is still influential today.
I am aware of two variants of this design:
I do not know Idéal's model names for these variants - you could guess 'Course' and 'Tourisme' but you might be wrong.
Finally, I would note that the pulley wheels and their associated nuts and chain catchers on these Idéal derailleurs are extremely similar to those on Super Rapid derailleurs. I don't know if Idéal manufactured the Super Rapid derailleurs or vice versa or if both brands shared a third party supplier of these parts.
This is an example of the 'touring' double pulley wheel model. In this case the main sliding rod components are manufactured from bronze. I do not know if Idéal made an aluminium version of the touring model. Perhaps not, as on tour, strength tends to trump light weight.
Some other points to note are: