Earthquakes were not divine judgments. They were sound squeezing waves traveling through elastic solid matter.
In the newly excavated central ground-shaking vault at Depth Six Thousand, Giles Croft leveled the slate foundation pier with a hair-width bubble transit.
The heavy slate slab was decoupled from the surrounding cave floor by a four-inch trench filled with dry river sand, preventing shaking from passing rail cars from corrupting the delicate clockwork needles.
Mounted atop the slate were two level swinging weight seismographs.
Each device featured a two-hundred-pound tube-shaped lead mass suspended on a high-pulling piano wire from an inverted three-sided steel frame.
At the tip of the level boom, an ultra-fine sapphire metal pen rested against a rotating drum covered in soot-blackened paper. It was driven by a care clockwork gear catch that advanced the paper at exactly one tiny fraction of an inch per second.
Beside Giles stood Maeve Swift-Ear, her brass ear-trumpet resting on a velvet-lined wooden tray.
Her keen vulpine ears were twitching in sync with the subtle, deep-hum shaking through the rock.
