Rare antique U-shaped horseshoe shaped Crookes tube cathode Wimshurst

On Offer here is this rare and very unusual, U-shaped horseshoe shaped cathode ray tube. 32 cm long by 21 cm across. Upright verticals is 16 cm. This unusual example was in the collection. I thought this old dozens of these over the years and this is the first time I've ever seen this U-shaped tube.

If anybody knows, its correct name would be interested in finding out. It consists of two vertical cylinders which turned 90° through a complete new shape tube The electrodes are at the tops of the vertical tubes, and there is a small metal ball inside the U-shaped tube, which I imagine has a reaction of some kind.

It sits on a wooden ebonised base.

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