In spite of myself I laughed.

“The second half of the film has never been exposed at all,” I rejoined.

“How can you prove that?”

“Very easily.  If I had ruined it by exposing it to the light as you suggest, the film upon development would have come out black!  But it is quite transparent!” I replied in triumph.

My retort floored the Court.  We were dipping into matters about which they were completely ignorant.  There was a hurried whispering and then the Chairman commented: 

“We’ll soon prove that you are wrong!”

Proceedings were suspended.  A clerk left the room to return a little later with a civilian who proved to be a photographer in Wesel.

The problem was presented to him, but I saw at once that he knew nothing whatever about the chemistry of photography.  He was turned over to me for cross-examination, and within three minutes I had so pulverised his statements that he was quite bewildered, and he left the Tribunal with his photographic reputation sadly shattered.

Another witness was summoned, the Court being determined to get at the bottom of the problem which had been raised.  They certainly recognised the significance of my contention.  This time it was a military officer.  He was examined by the Court, and then I was given the liberty to cross-examine.  My very first question was adequate to satisfy myself that he knew even less about the subject than the previous witness.  But he was nervously anxious not to betray his ignorance.  He had been called in as an expert and fervently desired to maintain this reputation.  He did so by acquiescing in every statement which I put to him concerning the action of light upon nitrate of silver.

“Now,” I asked emphatically, when I had completely caught him, “under these circumstances, and according to what you have been explaining to the court, the second half of this film which is transparent has never been exposed?”

“It has not.”

His negative was so emphatic as to convince the Court.  I had scored the crucial point and felt, now my supreme difficulty had been subjugated so conclusively, that all was plain sailing.  It was only too evident that everything had turned upon that short length of unexposed film, and I felt devoutly thankful to Providence that the light had not accidentally penetrated to the sensitised surface.  Had the unexposed section been black my fate would have been irrevocably sealed.

Now I was asked to present my defence.

“Can you give us a complete and detailed narrative of your journey, say from the time you left Brighton by the 5.10 p.m. train, on Saturday, August 1, up to your arrest.”

I nodded affirmatively.

“Well, go ahead!”