The gauge does not have opinions. That is why I keep it. – E. Pellow, Pressure House
The Breath is gas. It is not a spirit, a sigh or a mercy, whatever you hear at the Great Sporocarp, and it is not inexhaustible, whatever you hear at the Exchange. It rises from fissures in the bed of the Sound in strings of bubbles, which the divers call beads, and it burns with a clean yellow flame that smells of nothing once it is lit. There are four hundred and twelve capped seeps in the Gaslit Reach. Each one is a pipe, a valve and a diver's knot, and each one runs, through mains laid along the quays, to the Pressure House on the Undertide Docks, where it is measured before it is allowed to become light. The Pressure House was built in 1862 to stop the lamps of the Upper Galleries going dim every time the tide went out. Its hall holds forty brass gauges in four rows, one for each district main and the rest for the great seeps, and they rise and fall with the water like the chests of sleepers. At high tide the Breath presses hard; at low tide it eases. A good engineer can tell the...
From the lore of The Gaslit Reach.