POLTON’S revelation gave us both a good deal of material for thought, and, naturally, thought generated discussion.

“How does Polton’s discovery impress you?” I asked. “Is it a real one, do you think, or is it possible that he has only found a mare’s nest?”

“We must wait until we have seen the model,” Thorndyke replied. “But I attach great weight to his opinions for several reasons.”

“As, for instance —?”

“Well, first there is Polton himself. He is a profound mechanician, with the true mechanician’s insight and imagination. He reads a certain function into the machine which he has mentally reconstructed, and he is probably right. Then there is the matter which we were discussing recently: the puzzling, contradictory nature of the case. We agreed that the whole group of events looks abnormal; that it suggests a connected group of events, intentionally brought about, with an unlawful purpose behind it, but there is not a particle of positive evidence connecting anyone with those events in the character of agent. The crux of the matter has been from the first the impossibility of connecting Haire with the outbreak of the fire. His alibi seemed to be unchallengeable; for not only was he far away, days before the fire broke out; not only, was there no trace of any fire-raising appliance; but the presence of the other man in the rooms seemed to exclude the possibility of any such appliance having been used.

“But if Polton’s discovery turns out to be a real one, all these difficulties disappear. The impossible has become possible and even probable. It has become possible for Haire to have raised the fire while he was hundreds of miles away; and the appliance used was so ordinary in appearance that it would have passed unnoticed by the man who was living in the rooms. If Polton is right, he has supplied the missing link which brings the whole case together.”

“You speak of probability,” I objected. “Aren’t you putting it too high? At the most, Polton can prove that the mechanism could have been used for fire — raising; but what is the evidence that it was actually so used?”

“There is no direct evidence,” Thorndyke admitted. “But consider all the circumstances. The fire, itself, looked like the work of an incendiary, and all the other facts supported that view. The fatal objection was the apparent physical impossibility of the fire having been purposely raised. But Polton’s discovery — if we accept it provisionally — removes the impossibility. Here is a mechanism which could have been used to raise the fire, and for which no other use can be discovered. That, I say, establishes a probability that it was so used; and that probability would remain even if it could be proved that the mechanism had some legitimate function.”

“Perhaps you are right,” said I. “At any rate, I think Blandy will agree with you. Is he coming to the demonstration?”

“Yes. I notified him and invited him to come. I couldn’t do less; and, in fact, though I have no great love for the man, I respect his abilities. He will be here punctually at eight o’clock to-night.”

In effect, the inspector was more than punctual, for he turned up, in a state of undisguised excitement, at half-past seven. I need not repeat his adulatory greeting of my colleague nor the latter’s disclaimer of any merit in the matter. But I noted that he appeared to be genuinely grateful for Thorndyke’s help and much more frank and open in his manner than he had usually been.

As the demonstration had been arranged for eight, we occupied the interval by giving him a general outline of the mechanism while he fortified himself with a glass of sherry (which Thorndyke had, in some way, ascertained to be his particular weakness) and listened with intense attention. At eight o’clock, exactly, by Polton’s newly-completed regulator, the creator of that incomparable time-keeper appeared and announced that the model was ready for inspection, and we all, thereupon, followed him up to the laboratory floor.

As we entered the big workroom, Blandy cast an inquisitive glance round at the appliances and apparatus that filled the shelves and occupied the benches; then he espied the model, and, approaching it, gazed at it with devouring attention.

It was certainly an impressive object, and at the first glance I found it a little confusing, and not exactly what I had expected; but as the demonstration proceeded, these difficulties disappeared.

“Before I start the movement,” Polton began, “I had better explain one or two things. This is a demonstration model, and it differs in some respects from the actual mechanism. That mechanism was attached to an eight-day clock, and it moved once in twenty-four hours. This one moves once in an abbreviated day of thirty seconds.”

“Good gracious!” exclaimed Blandy. “How marvellous are the powers of the horologist! But I am glad that it is only a temporary arrangement. At that rate, we should all be old men in about twenty minutes.”

“Well, sir,” said Polton, with an apologetic and crinkly smile, “you wouldn’t want to stand here for five days to see it work. But the calendar movement is exactly the same as that in Mr. Haire’s clock; in fact, it is made from the actual parts that I found in your box, excepting the two wooden drums and the ratchet pulley that carries the cord and weight. Those I had to supply; but the spindle that carries the drums, I found with the star-wheel on it.

“As we haven’t got the clock, I have made a simple little clock to turn the snail, like those that are used to turn an equatorial telescope. You can ignore that. But the rest of the movement is driven by this little weight, just as the original was. Then, as to the addition that someone had made to the calendar, I have fixed the week-snail to the end of the spindle. I don’t suppose that is how it was done, but that doesn’t matter. This shows how the snail and pallet-bar worked, which is the important point.”

“And what is that contraption in the bowl?” asked Blandy.

“That,” Polton replied a little evasively, “you can disregard for the moment. It is a purely conjectural arrangement for starting the fire. I don’t suggest that it is like the one that was used. It is merely to demonstrate the possibility.”

“Exactly,” said Blandy. “The possibility is the point that matters.”

“Well,” Polton continued, “that is all that I need explain. I have fitted the little clock with a dial and one hand so that you can follow the time, and, of course, the day of the week and the day of the month are shown on the two drums. And now we can set it going. You see that the day-drum shows Sunday and the date-drum shows the first, and the hand on the dial shows just after three o’clock; so it has just turned three o’clock on Sunday morning. And, if you look at the week-snail, you will see that it is set to discharge on the fifth day — that is, at three o’clock on Friday morning. And now here goes.”

He pulled up the little weight by its cord and released some sort of stop. Forthwith the little conical pendulum began to gyrate rapidly, and the single hand to travel round the dial, while Polton watched it ecstatically and chanted out the events as they occurred.

“Six a.m., nine a.m., twelve noon, three p.m., six p.m., nine p.m., midnight.”

Here he paused with his eye on the dial, and we all watched expectantly as the hand moved swiftly towards the figure three. As it approached there was a soft click accompanied by a slight movement of the two drums. Then the hand reached the figure and there was another click; and, immediately, the two drums turned, and Sunday, the first, became Monday, the second.

So the rather weird-looking machine went on. The little pendulum gyrated madly, the hand moved rapidly round the dial, and at each alternate three o’clock there came the soft click, and then the two drums moved together and showed a new day. Mean while, Polton continued to chant out his announcements — rather unnecessarily, as I thought, for the thing was obvious enough.

“Tuesday, the third; Wednesday, the fourth; Thursday, the fifth, six a.m., nine a.m., noon, three p.m., six p.m., nine p.m., midnight — now, look out for Friday morning.”

I think we were all as excited as he was, and we gazed at the dial with the most intense expectancy as the hand approached the figure, and the first warning click sounded. Then the hand reached the hour mark, and, immediately, there was a double click, followed by a faint whirring sound; and suddenly a cloud of white smoke shot up from the bowl and was instantly followed by a sheet of flame.

“My word!” exclaimed Blandy, “there’s no nonsense about that. Would you mind showing us how that was done, Mr. Polton?”

“It was quite a simple and crude affair,” Polton replied, apologetically, “but, you see, I am not a chemist.”

“The simpler, the better,” said Blandy, “for it was quite effectual. I wish you had shown it to us before you let it off.”

“That’s all right, sir,” said Polton. “I’ve got another ready to show you, but I tho............