In A Nutshell Antiques and Interiors has dated this piece to the Victorian era.
On each side of the box are terminals where the metal probes are connected.

What makes this particular machine special is the raised dial on top of the box. It is housed in a brass mount, covered with bevelled glass. The paper dial has a metal pointer which is connected to the machine to measure the intensity of the current being generated. It also has the makers name "Joseph Gray & Co Sheffield. Improved Magnetic Indicator".

I have not attempted to test the machine as far as whether it generates a shock and it is being sold as seen. However I can confirm that all the parts move as they should, the dial moves and when a voltmeter is used on the terminals it does produce a current.

It is in good condition for its age and displays well. It has been cleaned and lightly polished and the box has been given a light wax to retain its aged patina. The box has picked up some scuffs and knocks and minor splits over the years and there is a chip on the glass covering the intensity dial but no major damages or anything detrimental. The drive band connecting the wheel to the coils is strong and still turns well. There is no key to the box.
The best description comes from the photos so please look at them all carefully and if you have any questions just ask.
Tracked UK delivery £10.
In A Nutshell Antiques and Interiors has dated this piece to the Victorian era.
Selling good quality victorian, georgian and earlier furniture, accessories & decorative items. Ashburton, devon. LAPADA member
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