"You continue to be wonderfully helpful. Thank you!" he says, with a little smile. Book of germ theory notes is retrieved, and he writes this down.

"You're welcome. Did I explain vaccination or just mention it...? I think I just mentioned it in passing. People throw off diseases that are caused by germs because there's a thing called an immune system in our bodies that figure out what things are germs - as opposed to just random stuff that isn't trying to hurt us - and kicks them out before they do damage. You might know of some diseases that you can only get once in your life? Chicken pox, maybe? Those are staying pretty much the same, so once you 'learn' what it looks like it never bothers you again. Other diseases change their details so you can get slightly different ones and be just as sick dozens of times. Colds are like that. And it turns out that if you take some germs that you've killed, or weakened - or even germs from a similar but less dangerous disease, in one case I can think of - and then you put them where your immune system can get a good look at it and easily beat it up, it'll know what to look for next time. Also, fun fact, allergies are what happens when your immune system gets the wrong idea about what things are germs and freaks out over nothing."

"Witches mostly don't get sick - I mean, we can, but it's highly unusual - so, yes, but not one I actually know about, because mostly it hasn't been researched, because the magic people are all pretty safe and their beloved humans only figured out what immune systems were fairly recently in spell development timescales."

"I'm going to have to invent like five new types of scrying just to figure out if mine can do it or not," he says, amused. "It's a good thing I like challenges, isn't it? If your magic can help, or fix it, then that would be fantastic, but I'll try mine. Since it's rather hard for me to test yours."

"It's not hard for witches who focus on magic - like me - to invent variants on spells that have been done, like when I brought the alethiometer I based the design on another summoning-an-object spell. But completely new things are harder. We have spells to cure diseases - witches get attached to mortals more than often enough to encourage that - but there's nothing for me to start from for boosting immune function unless it's brand-new and hasn't made it into my clan library yet."

"Oooh, that's handy. We haven't managed any spells to cure diseases, but broken bones and stab wounds and such some of us can do. Not me, personally, but I know a few who can. I have a bit of training, but apparently my teachers decided healing was not the kind of thing I should be able to do," he explains. "It's another thing I'm working on."

"Well, while I'm visiting I'll heal anybody with something I can cure who comes by if I have the materials for it - I won't be able to bring literally everything."

Isabella bursts out laughing. "Well. If you want to hug me I won't stop you, and you have already showered me with an alethiometer accessory that puts objective truth at my fingertips. So you and your excellent taste in people need not consider yourself too indebted when I tell you that witches avoid using money per se."

"Well, the stuffy scholars who inefficiently study non-missing alethiometers refer to them as 'artifacts', but that has the connotation that they're old and irreproducible, so your alethiometer accessories will not achieve the status for some time."

"Oh, well. There go my dreams of stuffy scholars calling something I made a thingamajig with a straight face. I'm crushed," says Adarin, not looking even remotely sad.

"Oh, I'm not planning to let them at the thingamajigs. They keep one of the alethiometers in a heavily secured glass case in an art museum, where it talks to itself and does nothing else of use, twenty-four hours a day."

He makes a face. "They don't even make a look-alike replica that's useless for truth-telling to replace it with? That way the alethiometer could still do something of use, but they can show off what it looks like? That's stupid. As the creator of the thingamajig, I'm going to veto anyone trying to put it in a museum if there aren't more thingamajig pairs than there are alethiometers."

Isabella giggles when he deploys the word "thingamajig" twice in a row. "Nah, the Louvre is big on authenticity and it's classifying the alethiometer as art. They have one in good condition and they are, I suppose, pretty."

"You have not seen some of what qualifies as art in some genres, I take it."

"Er. Probably not, no. Is this another thing I should be educated on?"

"I doubt it has any practical value, but it might amuse you. There are museums of modern art where the idea of 'modern' is so opaque and divorced from attempting elegance or appeal of form that it's literally possible to mistake janitorial equipment for an exhibit."

"Ah. That sounds confusing. I'll maybe go get educated on it, later, but for right now... Eeeeh. Janitorial equipment doesn't appeal, at the moment," he shrugs. "Is there another idea for how I should spend my between-spell downtime?"

"It's possible you should read an encyclopedia. Not cover to cover - maybe not even a paper one. I could take you to the library and you could go cruising through Wikipedia. Start with things that are in common use where you're from and proceed to whatever it says supplanted them."

"I have no idea what that is, but I agree that it'll be helpful!" he grins, then adds, "I'm going to get absurdly wealthy off of borrowing ideas that other people had and then using them to my own benefit, aren't I? That's completely diabolical, you're fantastic."