In the 1933, William Wettlaufer of Buffalo, New York was granted a Canadian patent on a "gravel treating apparatus" to screen and grade crushed stone, ores, coal and other materials.
In 1934, he patented a "gyrating mechanism" for a similar purpose. His machine eventually found application in Canadian coal mines to sift and separate grades of coal based on a shuffling action. Wettlaufter observed that a number of miners would come and sit or lean on the machine during their breaks, claiming that the vibration helped with their sore backs and muscles. He eventually developed a scaled-down version and patented it in 1941 but didn't take it to market. (He also patented a "vibratory therapeutic chair" in 1950, and helped his son-and-law develop a screening device that was the basis of the Derrick Corporation.) In 1948, Owen Murphy brought a prototype at an auction and subsequently patented his own version in 1958.
Out of this came Niagara Healthcare of Adamsville, Pennsylvania, today a large manufacturer of therapy products.
Monarch Massage is gone, but Niagara is still a going concern and still offers this device, which is based on cycloidal vibration therapy. However, as recently as November 2013, the company got into some trouble with the British Advertising Standards Authority Complaint Board over false and misleading advertising relating to these products.
As for the one I picked up, it still works beautifully and, on full setting, vibrates so fiercely that the dog starts growling and barking downstairs! I can't speak to its therapeutic efficiency, but I'm thinking it could be effective underneath a sealed plastic container filled with cleaning fluid for cleaning small parts in my shop.