The flickering trenches slid by and away; below us the earth had become calm, luminous blue, pricked here and there with yellow pin points of light; but still I thought I heard that measured, muffled beating as of a great drum, only presently it became harsher as though the drummer was wielding his stick with sudden fury, an insanely growing fury; and you felt a wind on your face, then it was gone, and you felt it again, for the aeroplane had begun to swing round in a slow circle, a nightbird you thought, seeking something below. And then again came the roars, two, one almost upon the other; they seemed ahead on our right somewhere; and again I felt the wind on my cheek, but not again; we were flying straight now. By this time I thought I knew what Hals had planned. Those pausing, slow, swinging circles had been made in order to get the exact source of the sound, and now Hals was flying towards it--his object the location of one of the enemy's batteries, a new battery, I judged as yet unknown to the Germans, possibly the one that had dropped the shell on the yellow house. Now, had Hals known that the shell was from a battery just getting into action? Because they are men of air as well as of earth, have these soldier-fliers strange powers? I noticed that the tiny lights from what must be a farmhouse down there, had a way of increasing and as suddenly decreasing from two to four to two; and always the vanishing lights would be patches, not pinpricks, more vivid, too, as though they were not shone through glass, but came from doors that opened into illuminated rooms. And I was wondering why these doors always kept opening and closing. The place must be a brigade headquarters or something equally important. That was it! Soldiers were constantly coming and going. And as regularly appearing, these patches of light grew more lurid, and the guns raged on, I thought with a smile that the firing might well be the slamming of those farmhouse doors, for just then the two had perfectly synchronized--the sudden flaring lights, the faint sound of guns. And then it happened again, one upon the other, and I must have risen to my feet for it dawned upon me--There's the battery over there! Those lights that I thought were part of the farmhouse! Our motor seemed to thunder unnaturally loud then, again they flashed down there, again the faint boom tore up to us. "_Kollosal!_" Hals had spotted the French guns.