I found this patent today, interesting in that the USPTO now lists Frank Gordon's patent under 'similar devices.
Good find Alan. The inventor Phillip E. Ohmart was active in the field of nuclear and industrial instrumentation. He apparently passed away in 1964 at age 48, just as his patent was granted. His company Ohmart Corp was then acquired by the German company VEGA Grieshaber KG, still very much in business. Tucked away on their web site is a table of dielectric constants, the most comprehensive I've ever seen: https://www.vega.com/-/media/p…electric_constants_en.pdf