While arrangements were being made to visit the batteries, Lieutenant Puaux explained to me a method they had established at that point for measuring the altitude of hostile aeroplanes for the guns.

“At some anti-aircfaft batteries,” he explained, “they have the telemeter for that purpose.  But here there is none.  So they use the system of visee laterale, or side sight, literally.”

He explained it all carefully to me.  I understood it at the time, I think.

I remember saying it was perfectly clear, and a child could do it, and a number of other things.  But the system of visee laterale has gone into that part of my mind which contains the Latin irregular verbs, harmonies, the catechism and answers to riddles.

There is a curious feeling that comes with the firing of a large battery at an unseen enemy.  One moment the air is still; there is a peaceful plain round.  The sun shines, and heavy cart horses, drawing a wagon filled with stones for repairing a road, are moving forward steadily, their heads down, their feet sinking deep in the mud.  The next moment hell breaks loose.  The great guns stand with smoking jaws.  The message of death has gone forth.  Over beyond the field and that narrow line of trees, what has happened?  A great noise, the furious recoiling of the guns, an upcurling of smoke—­that is the firing of a battery.  But over there, perhaps, one man, or twenty, or fifty men, lying still.

So I required assurance that this battery was not being fired for me.  I had no morbid curiosity as to batteries.  One of the officers assured me that I need have no concern.  Though they were firing earlier than had been intended, a German battery had been located and it was their instructions to disable it.

The battery had been well concealed.

“No German aeroplane has as yet discovered it,” explained the officer in charge.

To tell the truth, I had not yet discovered it myself.  We had alighted from the machine in a sea of mud.  There was mud everywhere.

A farmhouse to the left stood inaccessible in it.  Down the road a few feet a tree with an observation platform rose out of it.  A few chickens waded about in it.  A crowd of soldiers stood at a respectful distance and watched us.  But I saw no guns.

One of the officers stooped and picked up the cast shoe of a battery horse, and shaking the mud off, presented it to me.

“To bring you luck,” he said, “and perhaps luck to the battery!”

We left the road, and turning to the right made a floundering progress across a field to a hedge.  Only when we were almost there did I realise that the hedge was the battery.

“We built it,” said the officer in charge.  “We brought the trees and saplings and constructed it.  Madame did not suspect?”

Madame had not suspected.  There were other hedges in the neighbourhood, and the artificial one had been well contrived.  Halfway through the field the party paused by a curious elevation, flat, perhaps twenty feet across and circular.