There was a group of what looked like metallic spheres appearing an vanishing over Maryland, seen from across the river in Virginia. They seemed to be floating, with something hanging from the back end of the sphere. There were numerous aircraft passing in between the observation point and the objects (it's very common for aircraft to pass by that point as it is a common approach to land at DCA) allowing a better assessment of the altitude of the spheres in question, about twice the height of the aircraft approaching to land.Most of the objects seemed to just be floating on an E/SE direction, two of the moved in the opposite direction and up and down rapidly before fading completely.