metallic disc silent no movement no windows

This is an historic sighting that was in november 1977 While waiting for a bus i noticed a metallic disc in a field approx 100metres away & approx 20metres in the air. At first i assumed it was a balloon advertising something.Just out of curiosity i moved towards it & there was no string,wire or tether holding it in place. There was a slight breeze but the disc was motionless & thats when i thought thats very odd.The disc was metallic in colour had no nuts,bolts,rivets nor joins visible.The disc was absolutely silent & was approx 4 metres diameter. I walked into the field staring directly underneath the disc.There was no movement it was absolutely still & silent.