midnight
They lurked in the buildings , permeating the solid walls , stalking through them , or down through the foundations ; they wandered upon invisible slopes of their own world , climbing up to gather in groups and hanging in mid-air over the city rooftops . In the Hudson River off Grant 's Tomb two or three hundred of the apparitions were seemingly encamped at a level below the river 's surface . And others were in the air over the waters of the upper bay . * * * * * Toward midnight , from the open ocean beyond Sandy Hook spectral vehicles came winging for the city . Rapidly decreasing what had at first seemed a swift flight , they floated like ghostly dirigibles over the bay , heading for Manhattan . The forts fired upon them ; airplanes darted at them , through them . But the wraiths came on unheeding .