In 1870's Trouvé conceived this portable electro-medical instrument. Not long ago, a surviving example of this went up for sale on eBay and was bought by an anonymous collector.
The only known surviving example of his frontal headlamp (1883) was unearthed in the reserve store of the Science Museum in London, while the only known surviving exampleof his portable electric safety lamp (1884) is on show at Teyler's Museum in the Netherlands.
Given that Trouvé was the inventor of the metal detector which has discovered treasure troves all over the world, there must be more examples of his electrical marvels,but WHERE?
Let the search continue!