Zeppelin Mystery

"Do you suppose that the Zeppelin was in difficulties, as she was flying so low?" Helen enquired. "It is a perfectly reasonable hypothesis," the Commandant assented. "Two patrol boats were sent out early this morning, in search of her. An old man whom I saw at Waburne declares that she passed like a long, black cloud, just over his head, and that he was almost deafened by the noise of the engines...