as mountebank, impostor, quack, and so forth,” suggested Thorndyke.
Mr. Penfield chuckled as he sipped his wine. “Your insight is remarkable,” said he. “You have quoted the very words. They complain that, after making a serious appointment with them and occupying their time, you merely asked a number of foolish and irrelevant questions, and then proceeded to sweep the floor. Is that an exaggeration, or did you really sweep the floor?”
“I collected a few samples of dust from the floor and elsewhere.”
Mr. Penfield consumed a luxurious pinch of snuff and regarded Thorndyke with delighted amusement.
“Did you indeed? Well, I am not surprised at their attitude. But a year or so ago it would have been my own. It must have looked like sheer wizardry. But tell me, have your investigations and floor-sweepings yielded any tangible facts?
“Yes,” replied Thorndyke, “they have; and those facts I will lay before you on the strict understanding that you communicate them to nobody. As to certain further inferences of a more speculative character, I should prefer to make no statement at present. They may be entirely erroneous.”
“Exactly, exactly. Let us keep scrupulously to definite facts which are susceptible of proof. Now, what have you discovered?”
“My positive results amount to this: in the first place I have ascertained beyond the possibility of any reasonable doubt that those boxes had been opened by some person other than Mr. Hollis. In the second place it is virtually certain that the person who opened them was in some way connected with Mr. Woodstock’s office.”
“Do you say that the boxes were actually opened in his office?
“No. The evidence goes to prove that they were taken from the office and opened elsewhere.”
“But surely they would have been missed from the strong-room?”
“That, I think was provided for. I infer that only one box was taken at a time and that its place was filled by a dummy.”
“Astonishing!” exclaimed Mr. Penfield. “It seems incredible that you should have been able to discover this—or, indeed, that it should be true. The seals seem to me to offer an insuperable difficulty.”
“On the contrary,” replied Thorndyke, “it was the seals that furnished the evidence. They were manifest forgeries.”
“Were they really! The robber had actually had a counterfeit seal engraved?”
“No. The false seal was not engraved. It was an electrotype made from one of the wax impressions; a much simpler and easier proceeding, and one that the robber could carry out himself and so avoid the danger of employing a seal engraver.”
“No doubt it would be the safer plan, and probably you are right in assuming that he adopted it; but—”
“I am not assuming,” said Thorndyke. “There is direct evidence that the seal used to make the false impressions was an electrotype.”
“Now, what would be the nature of that evidence—or is it, perhaps, too technical for an ignorant person like me to follow?”
“There is nothing very technical about it,” replied Thorndyke. “You know how an electrotype is made? Well, to put it briefly, the process would be this: one of the wax impressions from a box would be carefully coated with black lead or some other conducting material and attached to one of the terminals of an electric battery; and to the other terminal a piece of copper would be attached. The black-leaded wax impression and the piece of copper would be suspended from the wires of the battery, close together but not touching, in a solution of sulphate of copper. Then, as the electric current passed, the copper would dissolve in the solution and a film of metallic copper would become deposited on the black-leaded wax and would gradually thicken until it became a solid shell of copper. When this shell was picked off the wax it would be, in effect, a copper seal which would give impressions on wax just like the original seal. Is that clear?”
“Perfectly. But what is the evidence that this was actually done?”
“It is really very simple,” replied Thorndyke. “Let us consider what would happen in the two alternative cases. Take first that of the seal engraver. He has handed to him one or more of the wax impressions from the boxes and is asked to engrave a seal which shall be an exact copy of the seal which made the impressions. What does he do? If the wax impression were absolutely perfect, he would simply copy it in intaglio. But a seal impression never is perfect unless it is made with quite extraordinary care. But the wax impressions on the boxes were just ordinary impressions, hastily made with no attempt at precision, and almost certainly not a perfect one among them. The engraver, then, would not rigorously copy a particular impression, but, eliminating its individual and accidental imperfections, he would aim at producing a seal which should be a faithful copy of the original seal, without any imperfections at all.
“Now take the case of the electrotype. This is a mechanical reproduction of a particular impression. Whatever accidental marks or imperfections there may be in that impression will be faithfully reproduced. In short, an engraved seal would be a copy of the original seal; an electrotype would be a copy of a particular impression of that seal.”
Mr. Penfield nodded approvingly. “An excellent point and very clearly argued. But what is its bearing on the case?”
“It is this: since an electrotype seal is a mechanical copy of a particular wax impression, including any accidental marks or imperfections in it, it follows that every impression made on wax with such a seal will exhibit the accidental marks or imperfections of the original wax impression, in addition to any defects of its own. So that, if a series of such impressions were examined, although each would probably have its own distinctive peculiarities, yet all of them would be found to agree in displaying the accidental marks or imperfections of the original impression.”
“Yes, I see that,” said Mr. Penfield with a slightly interrogative inflexion.
“Well, that is what I have found in the series of seal-impressions from Mr. Hollis’s boxes. They are of all degrees of badness, but in every one of the series two particular defects occur; which, as the series consists of over thirty impressions, is utterly outside the limits of probability.”
“Might those imperfections not have been in the seal itself?
“No. I took, with the most elaborate care, two impressions from the original seal, and those impressions are, I think, as perfect as is possible. At any rate, they are free from these, or any other visible defects. I will show them to you.”
He took from a drawer a portfolio and an envelope. From the latter he produced one of the two impressions that he had made with Mr. Hollis’s seal and from the former a half-plate photograph.
“Here,” he said, handing them to Mr. Penfield, “is one of the seal impressions taken by me, and here is a magnified photograph of it. You can see that every part of the design is perfectly clear and distinct and the background quite free from indentations. Keep that photograph for comparison with these others, which show a series of thirty-two impressions from the boxes, magnified four diameters. In every one of them you will find two defects. First the projecting fore-legs of the left-hand horse are blurred and faint; second, there is, just in front of the chariot and above the back of the near horse, a minute pit in the back ground. It is hardly visible to the naked eye in the wax impressions, but the photographs show it plainly. It was probably
