Oval object seen hovering by highway 20 miles south of Fon du Lac

Father left written account of observed UFO traveling north on highway during business trip midday. He initially saw oval and dark shape inside of a cloud as he was driving. As he drew abeam of the cloud he pulled over and stepped out to observe. The shadow remained distinct and sharply defined inside cloud. The shadow and cloud appeared to be over high power-line near power pole about 100 to 150 yards in altitude. He then proceded to test his vision, turning away from the object and pinching himself on the leg. He tried to slow down passing traffic; gesturing and pointing at object. Nobody even slowed down. He walked around the car, taking his eyes off the object again; it was still there when he looked. Eventually, the object seemed to slowly emerge from the cloud, revealing to be a dull silvery disc approximately 30 feet wide. It had no lights, portholes, markings, or discernable seams. It made no sound, hovering with no visible support or moving parts. It wasn`t a perfect oval, it had a subtle eliptical shape that gave him an impression that it had a fore and aft. He also had the impression the object was approaching him and he quickly got into his car and sped off at a high speed; not knowing what the object eventually did or seeing it again.