“It’s the foghorn, or whistle,” replied Mr. Brown. “There is a thick blanket of fog all around the _Beacon_. The captain and the man on the lookout cannot see other ships coming near us, and the men on the other ships cannot see us. So, in order that we may not run into them, the foghorn is being blown. The other ships can hear it and steer to one side. Collisions at sea are very dangerous.”