Henri was giggling now, barely able to contain himself. "So I'm to shovel coal into my shoes hoping no one notices, while smoke and steam - what of the vapor?"
"There's little more smoke than a cigar, and the steam would be barely visible by gas lamp. It vents out the back of your trousers, under the tail of your coat."
"Marvelous!" said Henri. "I use a similar port for my own vapors. I want to try them, immediately.

Auteur: Christopher Moore