"Ah, but that we all could escape the circumstances of our birth. Why don't you come inside my humble home for a bit? At the back. I'll put on tea."

That actually worked?

"My name is Wey Fu, by the way, sorry for the lack of introduction."

He uses his real name, it isn't particularly unlikely as an Earth Kingdom name or common as a Fire Nation name.

He walks around to the back.

"I'm Shao Nin. Come on, then..."

The interior is cramped. An all in one living area with hardly any room to move between all the cunning boxes and cabinets. The table folds out of the wall, as does the bed. In fact, what was previously a display of items has become a shelf and desk on the interior as he folds things away. The boiler at the back is a weirdly bulbous thing, almost egg-shaped with a wide, flat structure on top and a large flywheel with linkages leading elsewhere right against the back wall, half covered by it. 

He draws near boiling water from a valve on the side, to make tea with.

"I have some sympathy for those who are born into a family that does not suit them." His tone is dry in a way that indicates he is part of this classification.

"Neither of us wants a mess, do we? Destruction, screaming, accusations, all that. Too troublesome to bother with."

“Yes.  I think both of us have clear incentives to keep each other’s situations private?”

Maybe he misread the situation  Shao Nin wasn’t accepting his offer, but rather wanted some privacy before refusing it?

“You can be assured of my discretion whatever your decision about my offer.”

Even with the seriousness of the situation, the boiler distracts him as he studies it and compares the design to Fire Nation designs he has studied.

It's clearly coming from almost an entirely different direction. The pancake shape is probably the working cylinder given the shaft and gearing connected to the flywheel, but it's far too wide and flat according to what Wey Fu knows. The device is not in motion right now.

He pours tea. Ordinary green, the kind that can be bought anywhere.

"I'm a misanthrope. I prefer my solitude, dealing with people is stressful, trust is a rare and precious thing that takes many moons to build and five seconds to destroy. I would prefer any deal we work out being clearly spelled out, even if there is no earthly authority either of us would be willing to go to in case of a dispute. You are implying that you are a firebender, correct?"

He wonders if the design is simply bad… or if it operates off subtly different principles than typical Fire Nation designs?  He’s really curious, but he needs to focus for now.

“That’s correct.  I lack the anger and hatred for powerful offensive Fire Bending-”

(Ever since witnessing his first massacre.)

“But give me metal that needs mending, a steam powered device that needs heat, or a furnace that needs stoking to just the right temperature and I can maintain a steady constant heat with the precision to rival a master.”

"A far better use of it in my opinion. Well, you want to get to Gao Lin and settle in there nice and quietly, I suppose. You'll need a story, and introductions... Do you know an ordinary trade? Carpentry, scribing, shoe-making or something like that? Smithing would be too much a risk."

"Hmm, smithing is probably my best non-bending trade, but yes too much of a risk of a subtle bit of automatic bending.  I'm able to handle bookkeeping and transcribing messages well enough, at least according to Fire Nation army standards.  I know the sorts of things a decent seaman knows... for steam-powered ships, not sailing."

He also has quite a bit more money they he showed to help get himself established, with two other purses concealed on his person (with soft material stuffed between the coins so they won't jingle), but he'll hold of on revealing that.

"Not many will trust you with their accounts when you're a fresh face. Transcribing messages and copying scrolls, might work. If you've a steady hand and produce good results, parchment and ink aren't cheap. Can you do arithmetic...? There's always the- No, you wouldn't want to get involved. Forget I said anything. So, to Gao Lin travelling together, introductions, and advice on a story to rely on, in exchange for... Information on engines and boilers, and some - assistance with fuel - and some coin. Does that broadly sound fair?"

He thought he was doing at least okay on a story... okay yes he needs help there.  And introductions could be invaluable for securing skilled work.  If the Avatar takes him time punishing the Fire Nation he could be in hiding for quite a few years.

"Yes, that sounds broadly fair.  Your boiler design is a bit different than what I'm familiar with... it shouldn't be a problem as long as your different design doesn't require a substantially higher maximum temperature than a comparable fire nation design.  And conversely, if you've figured out something with a lower heat requirement, I could do even better than I was expecting on saving you fuel.  ...It would be best if I could check how my fire bending interacts with your boiler and engine before we finalize the exact expectations on fuel I can save you."

He means this quite seriously (if he can replace almost all of the need for fuel, maybe he can get a better deal on the payment in coin)... but also he is really interested in seeing an entirely new boiler design, even if its unusual appearance turns out to be from bad design as opposed to something unprecedented or at least novel.

"Well, I have no idea how the Fire Nation does it but fuel is expensive so I tried quite hard to make it efficient. We can take a look when we finish this tea. No sense wasting it already poured."

Sip.

Is it poisoned?  If this man hates the Fire Nation and wants to kill him quietly so his own secrets aren't exposed, poison would be an option.  On the other hand, he will be trusting this man for a rather long journey with lots of opportunity for betrayal, so he'll have to trust him at some point.

Sip.

He smiles appreciatively.

"So... Story. You can not want to talk about it, that's understandable, and certainly don't volunteer information, but you'll want something to tell people. Ahem."

He affects a high-pitched fake voice. "Oh, you're fleeing the Fire Nation. Those bastards are ruining everything. Was your village destroyed? Are you looking for family? Maybe you can reunite with them here where it's safe! Where did you say you were from, exactly?"

"...And best not claim familiarity with a place you're not familiar with. Ahem."

"You know my great uncle on my father's side used to live in Omashu, you know, around the lower basalt district right near that one vegetable seller that always had eggplants out front, right under one of the delivery chutes- What do you mean 'what delivery chutes'? Are you REALLY from Omashu?"

More tea. Screwing around with voices makes him thirsty.

"Do you think being from a the village under long-term occupation by the Fire Nation would be too suspicious?  There are a number of them I could describe in elaborate detail, and I could likewise describe a plausible escalation in Fire Nation brutality and oppression that motivated me to leave in a hurry."

"Plausible, and preferably it was a real one that was really destroyed or at least gutted. You don't want to go into elaborate detail at the drop of a hat though. Being too rehearsed about it could be bad, too, people don't give their life story out to everyone. Remember your character- They grew up there, and the way that village lived was just normal, and the brutality was horrifying. And anything that makes people confused, differences in turns of phrase or holidays or which spirits to propitiate or what have you, was probably... Fire Nation propaganda eroding your heritage."

"Yes, I have just the place in mind..."

He doesn't want Shao Nin dwelling on exactly why he can remember brutalized and displaced Earth Kingdom villages so clearly... he should change the subject.

"So you said you could make a few introductions in Gao Lin?"

"Oh, sure. Shopkeepers, artisans, the head servants of a couple of local lesser nobles, my usual customers. I'm not gonna promise them the world, but I'll corroborate a tragic story and say you've got a head for writing and numbers if I observe these traits during our trip."

"I can definitely demonstrate those traits.  Hmm... related question, the mathematics with ratios and proportions the Fire Nation uses in it's steam engine designs and similar engineering.  Do I need to avoid showing that mathematical knowledge because it would be too obscure or foreign and thus suspicious, or does the Earth Kingdom have that sort of math also?  I don't know if, for example architects would also use it.  We should probably thoroughly go through mathematical and scientific nomenclature at some point if we don't cover it while I'm explaining my information about steam engines."

Hopefully he didn't just insult the man by implying the Earth Kingdom is backwards or whatever, but he needs to avoid revealing himself and forgetting himself while excitedly explaining some finer point of mathematics is the exact sort of mistake he is prone to making.

"Hard to tell, it's not like the Earth Kingdom doesn't produce any mathematicians or engineers? Maybe brush up on static force analysis and architecture. There's math that goes into large buildings, aqueducts, and the like, and that's a very Earth Kingdom-respectable sort of math."

It sounds like the Earth Kingdom has developed some branches of mathematics much further than the Fire Nation!  He had thought he had learned how to see through the Fire Nation's propaganda, but it seems like he still has a lot to unlearn and relearn.  An out-of-place deficit in knowledge might get him killed, but the excitement about the chance to learn some new math is outweighing his fear, at least for the moment.

"I would very much like to learn more about that sort of math."

He isn't bothering to conceal his excitement, this man is clearly an intellectual, at least in an eccentric loner sort of way, so hopefully he will sympathize with Fu's excitement, or at least not actively look down on him.

"It is quite interesting. The big one is various methods of approximating the total force acting on different parts of a large structure, derived through a method called the 'integral'. The usual example is a dam holding back a great mass of water..."

He can explain some of the not-quite-calculus that has been popular in higher end Earth Kingdom academic circles as they finish the tea. It suffers a bit from lack of writing material to demonstrate on, though.

This partnership is already paying off!

He follows as best he can.  He enthusiastically asks questions.  His questions aren't exactly the most insightful, but he does seem to be getting the concepts.  Some of his questions are a bit off-base, perhaps from a lack of writing material to put the concepts to paper, or perhaps because he is already looking for ways to extend the methods to more dynamic engineering problems, such as a steam engine in motion or a boiler holding steam.

Now that the tea is gone they can get out his chalk and slate and do the math more properly. And look at his engine.

"So, the key observation I have made is that hot air expands, and cold air retracts. This wheel here is big and heavy enough to keep everything moving along. It turns, The plate inside this box here moves up, and the air inside the exchanger moves to the side closest to the boiler. It gets hot, and expands. That makes this - piston over here - push out, which adds a little bit more energy to the wheel. Then, the wheel keeps turning. The plate moves down, and pushes most of the air in here to the cool side. It contracts. This piston is then driven to retract by the pressure, and again adds a bit of energy to the wheel. And then it moves up again, air to the hot side, expand... The big problem is making the system overcome friction without losing too much force, and that it's not all that powerful. Though it does seem to be a bit more efficient, heat-wise, than boiling steam from what I've been able to guess?"

"Air instead of steam... remarkable!  And it would obviously be less powerful yes... but you think it is more efficient?  Losing power for efficiency does seem like the sort of thing tradeoff Fire Nation might have easily overlooked considering properly."

He's excited.  He starts talking fast in his excitement.

"I can gauge how much heat I'm putting out almost exactly, like for a given mass of water I can raise it's temperature to an exact fraction of progress along the way to boiling.  And I have the numbers on a variety of Fire Nation steam engine designs, so we can get an exact comparison on power, uh assuming you already have a good way of converting your measurements of your engine's power into weight moved through a distance within a period of time.  Ah, to explain, I think that is the most promising method for generally expressing physical power, although there was some debate over alternate methods and there are a lot of imperfect methods to express power as heat.  The power as heat thing is a point of nationalist pride even though I think it is kind of stupid because you could always make a more efficient engine.  In fact, the standard conversion ratios kept getting rewritten to match the conversion of whatever the current most favored fleet flagship's steam engine had.  Kind of petty and stupid really.  If you ever publish your designs and reveal even greater efficiency and leap past a century of Fire Nation scholarship (tainted as it is by ego and an overly pragmatic military focus) and your design becomes the standard heat-power conversion ratio I am going to find that absolutely hilarious."

Well, find it hilarious assuming he isn't dead at the hands of an Earth Nation mob, but he'll let himself dream for the moment.

"...Weight moved through distance... I've been measuring force based on the rotation rate of the wheel, and increases and decreases to it. Getting it to help move the cart without completely stopping the wheel was tricky. A spinning wheel is, actually, an object in motion though... If you imagine it as a lot of bricks tied to ropes going around, I mean, the motion of all the individual bricks added up would be an integral, but now I'm wondering how to calculate that, I've never heard of it thought of that way before... That kind of nonsense with changing standards is why I don't go to Ba Sing Se's academic circles for help. They're all up their own noses in studying the ancient tomes and smiling patiently at the insane nonsense their juniors come up with."