I bought this unit several years ago from a car boot (swap meet). Thought it was a good time to see if it worked and what kind of voltage it could generate.
These are often considered as quack devices but really it is an early form of todays tens unit which also generates electrical impulses that can reduce the pain signals going to the spinal cord and brain and stimulate the production of endorphins.
I didn't try it on myself, when it mentions wetting sponges to reduce the tingling sensation, I thought better let my multi-meter take the brunt of it instead.
I believe this machine was manufactured by the Jerome Kidder Manufacturing Company in New York City as looking online they look almost identical including most of the text and images. The only difference is where most say Davis & Kidders on most, this one just says Improved at the top of the box with an illustration of an 1862 Londini Honoris Causa coin in the bottom left and right corners.
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Music by Mark Generous - Golden Hour - https://thmatc.co/?l=68BD4D50