It's the description by Neville Cardus which intrigues me the most;
More on what he bowled ...
It is ...at any rate clear that Barnes executed his leg break without turning the wrist, an action which gives some notice to the batsman. Appartently Barnes manipulated the leg turn mainly by leverage of the third finger - as most leg spinners do, though most of them need to twist over the wrist."
This probably explains his maintaing the seam position as would an inswing bowler so that the ball would swing inwards in the air and still break away on pitching.
....Mentally mingle the best of Tate and Bedser; length, pace, swing, then add a tincture of Orielly, then maybe some adumbration will emerge or loom of Barnes in full spate.
To flick the cricket ball in an anti-clockwise direction by moving the third-finger from 6 o'clock to 12 o'clock can be done (just) as I've just tried it. But I would hate to do it ALL day while bowling medium pace and aiming at exact spot 3 1/2 metres from the stumps. He must have had unusually large hands and finger muscles like iron.