The precious bag was now opened and the twenty-three cheques brought out and laid on the bench in a consecutive series in the order of their dates.  They were then fixed by tapes—­to avoid making pin-holes in them—­in batches of six to small drawing boards, each batch being so arranged that the signatures were towards the middle.  The first board was clamped to the easel, the latter was slid along its guides until the pointer stood at / 2 on the long-focus scale and Thorndyke proceeded to focus the camera with the aid of a little microscope that Polton had made for the purpose.  When Mr. Britton and I had inspected the exquisitely sharp image on the focusing-screen through the microscope, Polton introduced the plate and made the first exposure, carrying the dark-slide off to develop the plate while the next batch of cheques was being fixed in position.

In his photographic technique, as in everything else, Polton followed as closely as he could the methods of his principal and instructor; methods characterized by that unhurried precision that leads to perfect accomplishment.  When the first negative was brought forth, dripping, from the dark-room, it was without spot or stain, scratch or pin-hole; uniform in colour and of exactly the required density.  The six cheques shown on it—­ridiculously small in appearance, though only reduced to half-length—­looked as clear and sharp as fine etchings; though, to be sure, my opportunity for examining them was rather limited, for Polton was uncommonly careful to keep the wet plate out of reach and so safe from injury.

“Well,” said Mr. Britton, when, at the end of the seance, he returned his treasures to the bag, “you have now got twenty-three of our cheques, to all intents and purposes.  I hope you are not going to make any unlawful use of them—­must tell our cashiers to keep a bright look-out; and”—­here he lowered his voice impressively and addressed himself to me and Polton—­“you understand that this is a private matter between Dr. Thorndyke and me.  Of course, as Mr. Blackmore is dead, there is no reason why his cheques should not be photographed for legal purposes; but we don’t want it talked about; nor, I think, does Dr. Thorndyke.”

“Certainly not,” Thorndyke agreed emphatically; “but you need not be uneasy, Mr. Britton.  We are very uncommunicative people in this establishment.”

As my colleague and I escorted our visitor down the stairs, he returned to the subject of the cheques.

“I don’t understand what you want them for,” he remarked.  “There is no question turning on signatures in the case of Blackmore deceased, is there?”

“I should say not,” Thorndyke replied rather evasively.