"Tallie," said the Book, "you will contact the Volto-Vac sales office and order two of their Chemical Communication Analyzers." Rosie had never heard of those machines, but when the Book explained that they interpreted chemical vapors as language she started to see where this was going.
"That difference engine of yours. It's some kind of decoding device...?"
The Book would have nodded, she was sure, if it had been built that way. "That part of my mechanism uses pattern recognition to decipher unknown tongues. It can store a great deal of information: then it looks through that data, establishes patterns, and eventually learns an entirely new language."
Rosie was nodding now even if the Book couldn't. "So you use it to interpret the unknown signals coming through the CCA and make sense of them. Yeah, I see it." She thought for a moment. "So if I use those two devices together I can analyze the way Henry's engine is working and he can actually hear it, as though it was talking to him." She kept thinking.
"And then once the difference engine has 'learned' the language of Henry's engine I can remove it. The CCA alone will do everything Henry needs. With a new CCA I could use the gadget as a general purpose diagnostic tool ...."
The Book raised its hand. "Exactly," it said. "When someone's engine malfunctions, it will be able to tell you why."
Rosie smiled. "Yep. We've got a deal, all right."
Then she thought again. "What was that other gadget you wanted?" And the Book told her.