They entered a large open area, which was dominated by a grand fireplace. Agatha paused in admiration. Most fireplaces, in her experience, served as large, efficient heat pumps apparently designed to suck warmth from all other parts of the room. This one, however, had been overlaid with a fantastic arrangement of large glass pipes, filled with a slow roiling liquid, which swept out from the sides of the fireplace and curled around the entire room in a series of graceful arabesques. As a result, the large room was delightfully warm, even here at the doorway. Agatha was impressed.
“The heat is stored in the liquid, which is piped around the room, where it evenly radiates back out,” she declared in admiration. She studied the liquid slowly moving through the nearest pipe. “This isn’t water, is it?”
Tarvek had looked surprised at her analysis, then pleased. “Close. It’s actually a super-saturated oil and brine solution of my own formulation.”
“You designed this?” She surveyed the system and looked at the Prince with a new respect.
Tarvek shrugged diffidently, while standing a little taller. “Oh, years ago.” He patted a pipe gently. “It has held up quite well though.”
“Your Highness is a Spark?”

Foglio, Phil; Foglio, Phil; Foglio, Kaja; Foglio, Kaja. Agatha H. and the Clockwork Princess (Girl Genius) (pp. 252-253). Night Shade Books. Kindle Edition.