The observatory at Avu, in Borneo, stands on the spur of the mountain. To the north rises the old crater, black at night against the unfathomable blue of the sky. From the little circular building, with its mushroom dome, the slopes plunge steeply downward into the black mysteries of the tropical forest beneath. The little house in which the observer and his assistant live is about fifty yards from the observatory, and beyond this are the huts of their native attendants.