These TV screen magnifying lens had their heyday in the 1940s and 1950s during the early years of television. They were sold by companies to fit screens that ran from 3″ to 12″ in diameter. They allowed for various ways of attachment to your black and white TV set: from the top, sides and bottom, on floor stands. Some even came in different colors – an early mimic of color TV, perhaps.
Most of the magnifiers were made of plastic or Plexiglass, according to the website, and some were filled with oil, water or some other liquid. The one at auction appeared to be filled with a liquid of some sort. Some TV sets also came with their own built-in magnifier.