Darwin unfolded the sheet and held it close to one of the candelabra, while the other four crowded around. The main line drawing was in green ink and filled half the sheet. An expanded detail of one part was shown above.
“I have seen it for myself,” Solborne said. “This is accurate as to both layout and proportion. Here on the flat upper surface”—he touched the upper part of the sheet—“you see nine keys or levers. Here are nine more. Each lever has ten possible settings, for the numbers zero through nine. Thus it is possible to define two numbers, each with up to nine digits. This is an eight-way lever which controls the operation of the engine. Addition, subtraction, multiplication, division, and the extraction of roots up to fifth order. And here”—he touched the paper again—“is where a number of up to eighteen digits appears. It is contained on a strip of paper, and it is printed, as by controlled type.”
“Are these dimensions accurate?” Darwin was crouched with his nose almost to the paper.
“They are. The whole engine, including its base, is two feet wide, three feet deep, and rather less than three feet high. It is also heavy, ten stone or more.”
“Ah.” Darwin leaned back, his face sad and oddly disappointed. “Then I am obliged to question the inventive genius of Professor Anton Riker. There was, eight years ago, on display in the court of Emperor Joseph of Austria—”
“The automaton chess player of Baron Wolfgang von Kempelen, which took the form of a seated Turk.”
“You know of it.”
“Certainly. It was no automaton, but relied upon a hidden accomplice. The device was otherwise impossible.”
“I am not persuaded of that. Before von Kempelen’s secret was revealed, Mr. Solborne, I wasted an inordinate amount of my time and foolscap seeking to define a possible mechanism. I was unable to prove that such a chess-playing machine is impossible theoretically; only that it would be prodigious complicated, and probably enormous in size.”
“Those observations would be yet more true of this ‘calculating engine.’ Dr. Darwin, my first response was yours exactly. This new machine, like the chess automaton, must be operated by some confederate of Professor Riker.
“Helen soon convinced me otherwise. First, the machine stands alone, not on some specially constructed dais or platform able to conceal a man. It works in bright light, with everything visible, rather than in obscuring gloom. The von Kempelen device was operated using a system of balls and magnets, impossible in this case. Finally, and far more important, consider what the engine does: the printed output is the result of a difficult arithmetic calculation, and it normally appears within thirty seconds of the complete statement of the problem. The input numbers are provided not by Riker, but by the audience—I have done it myself. There is no way that an assistant could know the problems in advance. Even with the use of tables, it would be impossible to provide the cubic root or quartic root of a nine-figure number, or the product of two such numbers, so quickly.”
“True enough.” Darwin pouted his full lips. “So, we have a mystery.”
He seemed ready to settle back into brooding silence, but Solborne would not allow it. He took the sheet from Darwin and returned it to his jacket pocket.
“A mystery, perhaps, but not the mystery. I would not travel so far afield, in winter, merely for the sake of some calculating device. My concern is with Helen, and Professor Riker. I already told you that I did not care for him, and I requested to Helen that his stay at Newlands not be an extended one. He and his machine departed three days after their arrival, during which time he offered me numerous demonstrations of the engine’s power. Then he left—but he did not go far. He rented a small house along the cliff, less than half a mile from Newlands, where he lives alone. And from that day forward, I saw the decline in Helen.”
“Melancholic?”
“Not at all. I saw—and see—physical decline. She has been losing weight, steadily. She was always fair, but now her skin seems almost translucent. Her eyes are set deeper in her head, and the skin beneath them appears to be almost purple, as though bruised.”
“And her manner?”
“Febrile, intense, yet cheerful. She seems distant from me, in a way that I have never before experienced. When I ask concerning her health, she says only that she is feeling tired, and does not seem able to get enough sleep. That is certainly true. She will nod off during dinner, or as soon as she sits down in a chair. I wonder what is happening.”
It was Darwin’s turn to hesitate. “Mr. Solborne,” he said at last. “It pains me to suggest this, but I assume that the obvious explanation has occurred to you?”
“That Helen and Riker are romantically engaged, and she spends her nights with him? Of course. It is not the case.”
“How do you know?”
“By taking an action that was not strictly honorable. As I told you, the main body of Newlands, including parlors, guest bedrooms, living room, dining rooms, and servants’ quarters, is of brick. However, there are two towers of stone, one to the north and one to the south side, rising from the main house. I have a suite of rooms, including my bedroom and study, in the north tower. Helen occupies the southern one, with her bedroom and parlor and sewing room. There are two entrances to each tower. One leads through to the main body of the house; the other, seldom used and originally built I suspect for use only in case of fire, leads directly outside, onto a path that runs along the cliff. It runs, in fact, to and past the house rented by Anton Riker. Suspecting Helen’s actions, I did two things. First, I placed locks on the outside of the tower doors. No one could then enter or leave Newlands without passing through the main body of the house. The only window in the south tower that can be opened wide enough to admit a person is near the top, overlooking a forty-foot sheer drop to stony ground.
“Second, I moved Joan Rowland, one of the servants who happens to be an unusually light sleeper, to a bedroom next to the inner door of the south tower. She was instructed to tell me if she heard any comings and goings at night.”
“And did she?”
“Not a one. She said that she heard Helen—or someone—moving around in the tower, often late at night when the rest of the house was asleep. But Helen never left her own quarters.”
“A necessary condition for chastity, but not a sufficient one.” Darwin stirred in his chair. “Mr. Solborne, when I was a student at Cambridge, it constantly baffled me that there was a rule forbidding the presence of ladies in college at night, while open access was permitted to any woman during the day. An odd assumption seemed at work: that improprieties take place only at night. What of your sister’s movements during the daylight hours?”
“Dr. Darwin, Jacob Pole warned me of your prescience. You are a mind reader.”
“Not at all. I merely seek to close logical loopholes. During the day?”
“At close of day, which in this season means between four and five o’clock, Helen leaves Newlands and walks south along the cliff.”
“To the house rented by Professor Riker?”
“That was my original assumption, that there was some sort of assignation involved. But it is not the case. As she walks south, he walks north along the shingled cliff to meet her. They stand in full view and talk to each other for five or ten minutes as darkness approaches. They just talk. They do not touch. Before it is fully dark, they part, and she returns home.”
“You have been spying on them?”
“I am very worried about my sister. Daily she has grown more pale and tense, more wan and bloodless.”
“And now we have one more mystery to consider. Timing.” Darwin did not elaborate, but leaned forward in his seat and thoughtfully cut a wedge of Stilton. The room fell silent, except for the sound of steady munching and the wheeze of James Watt’s asthmatic breathing.