Nod. "Sounds good." 

More trials! Abras takes copious notes, both on the measurements and on potential sources of noise.

Sandra gets out a big canvas and charcoal, and tries drawing their points on a graph. "Huh. Neat." She grins at Abras. 

"Ooh, that's a lot easier to interpret than just the numbers. It could definitely be a straight line with some measurement errors. Oh, and I just had another thought--does it go the opposite way? I mean, if you take a container of air and squash it smaller, does it heat up?"

"Oooh! Good question. How would you want to test that, to get any precision?" 

"I could try holding the air in a barrier shield and then shrinking it? If we can get good measurements of the size of the barrier. Maybe if I made it a cube."

"And then just guessing at how much warmer it seems? I suppose if all we're curious about is yes or no on 'does it heat up' then that'd be precise enough." 

"Yeah, if it turns out to heat up at all I'd want to find out how much. Do you know of any materials that respond to small temperature changes in predictable ways?"

"Oooh! Not off the top of my head, but I'll have to think about it. Can ask Savil too." 

"Good idea. Anyway, shall we try squeezing some air?"

"Yes, let's!" Sandra leans forward, eagerly watching. 

He makes a cubical shield about half as long as he is tall, one that doesn't let air through, and tries squashing it in just the vertical dimension without letting any air escape, while paying attention to how much it pushes back. He'll stop when it gets to half the original volume or when something concerning happens.

Abras is pretty powerful and his shields are strong; nothing concerning happens, though the shield-spell does start to gradually drain more power from him. 

When he lets a little bit escape, it's notably hotter, like the air from right over a campfire.

"Whoa!" Sandra breathes. "This is so fascinating. We should show Savil." 

"I have no idea if it's useful for anything but it's pretty neat!"

"I wonder if you started with a really big barrier and squished it a lot, you could get it to do the explode-y thing that the weather barrier did?" 

"It does seem like it ought to have the same effect. We could theoretically try it sometime if you wanted to, Savil and I found a good place by the river."

"I think I'd like that! I'm so curious." Sandra looks thoughtful. "I wonder if there are other things that get - bigger, I guess, when they're hot. If there were liquids that did that, you could maybe see how high up a glass they went? ...A skinny glass. But I don't think water gets bigger when it's hot, at least I've never noticed it." 

"That's a good idea. But yeah, if water does that it does it too slowly to notice. But there might be some liquid that's more like air that way."

"Other liquids, hmm. Wine? I guess that's still mostly water. Brandy?" 

"It's worth checking; I haven't paid enough attention to brandy to notice either way."

"What other things are liquids... Umm, oil? Candle wax, I guess, but only when it's already hot? ...Hmm. Butter melts when it's only a little warm. If we can think of enough things that melt or go solid with different temperatures, we could put them in a row and at least get an estimate that way." 

"Is going solid actually necessary? Air does the thing we need without going solid, it just doesn't stay put. I think the ideal thing would actually be something that stays liquid no matter how cold it gets and just keeps shrinking."

"I think brandy doesn't freeze? My da used to go put it in a snowbank outside because he liked it chilled."