THEY LOOK LIKE a cross between a tepee and a corn-mash still and there are two of them in A. P. Thomson's orchard. A small sign at the base of each reads "Ortho- molecular Multi-wave Oscillator."

Thomson admits they look silly. "We put some on our demonstration farm (operated by Natural Foods Associates, a group Thomson heads) in Texas, and the man who manages the farm said, 'This has gotta be the biggest con game there ever was.'

They are based on research by Dr. Philip Callahan of the University of Florida, who studied ancient stone silos in Ireland built by Christian monks between the fifth and seventh centuries. The silos contained metallic ore that could collect and resonate radio energy from the sun -- in the 1 million- megacycle range. Callahan thinks ancient farmers used the silos to spur the growth of crops.

"Now, we are doing the same thing with these oscillators made of copper pipe," says Thomson, who won't say yet if it is working for his apple trees. But Joseph Francis, the manager of the demonstration farm, is a convert: "We just finished harvesting four times more hay out of that field than we ever got before." Francis says he is "quite surprised," adding, "I believe now that if I was just starting a farm, these oscillators would be the first thing I would get."