“What is the object of photographing these cheques?” I asked.

“There are several objects. First, since a good photograph is practically as good as the original, when we have the photographs we practically have the cheques for reference. Then, since a photograph can be duplicated indefinitely, it is possible to perform experiments on it which involve its destruction; which would, of course, be impossible in the case of original cheques.”

“But the ultimate object, I mean. What are you going to prove?”

“You are incorrigible, Jervis,” he exclaimed. “How should I know what I am going to prove? This is an investigation. If I knew the result beforehand, I shouldn’t want to perform the experiment.”

He looked at his watch, and, as we rose from the table, he said: