TITLE Kettlewick Observatory — Seismograph No. 2 PROMPT A live drum seismograph for a fictional observatory: a clockwork cylinder wrapped in paper turns slowly beneath a pen on a long boom, which draws a continuous wiggling trace; the trace advances one line down the sheet each revolution, building the classic helical record of an observatory "day". The ground is quiet apart from microseisms, the occasional fictional distant earthquake, and the viewer: tapping or shaking the page is recorded by the instrument. Concept: a dashboard made of one instrument and its paper, where the viewer's own actions become data. Mood: attentive, old-fashioned, humane science. Palette: recording paper #F1EBDD, pen ink black #1F1F1F, observatory red #B3261E for time marks, annotations and alarm, instrument slate blue-grey #4C6A7A for metalwork; brass touches allowed in the mechanism only (#B08D3C). Light page. Composition: upper portion: the instrument in elevation, drawn in SVG/canvas: the drum (a cylinder shaded with a vertical gradient, paper wrapped around it, visible seam, end caps and a clockwork gearbox with a slowly turning escapement), the pen arm with its pivot, counterweight and a fine stylus touching the drum, damping vane in an oil pot, and the mass on its spring frame. Lower, larger portion: the unrolled sheet: the "seismogram" as a flat chart of parallel trace lines (each line representing one minute in accelerated observatory time at the standard drum speed, six times faster than real time; 26 lines visible), with red minute ticks made by the time-marker (a small lift in the trace every minute), hour labels at the left margin written in a neat hand, and the newest line being drawn live at the bottom with the pen position shown as a small red index. When the sheet fills, it scrolls up and the oldest lines leave. Signal model: baseline microseism noise (band-limited noise with slow amplitude swells, like ocean storms); a fictional teleseism every few minutes (generated with a seeded schedule from the real clock so it is the same for a given hour): a sharp small P-wave onset, a gap, a larger S-wave, then long rolling surface waves that grow and decay over many seconds, with a coda; local "events" from the viewer. The pen is simulated as a driven damped oscillator (so sharp inputs ring down realistically) and can clip against its stops with a visible flat-topped trace on very large shakes. Interaction (signature moment): tap, click or thump anywhere on the page (or press the Space bar; on phones, tapping the screen) and the instrument registers it: the whole page gives a tiny shudder, the pen arm kicks, and the trace records a spike that rings down; rapid tapping builds resonance; dragging the mouse fast "shakes the building". A "strike the pier" mallet control gives a calibrated pulse. When a larger event occurs the dashboard reacts: phase arrival flags are pinned to the trace as it is drawn (red "P", "S", "L" letters with hairlines), a distance estimate is computed from the S-minus-P time ("S − P = 41 s → about 380 km"), a magnitude estimate from amplitude appears on a small nomogram where a line connects distance and amplitude scales, and a telegram-style slip is typed out: "KETTLEWICK 0417 GMT · MODERATE SHOCK · DIST 380 KM · BEARING UNKNOWN (ONE STATION)". Each event is added to a ledger table (time, S−P, max amplitude in mm, remark), with the viewer's taps logged as "local disturbance (visitor)" with dry remarks. Side panel readouts in analog style: drum speed, paper remaining as a dwindling roll, pen ink level, a small 24-hour dial of observatory time, a "station noise" needle gauge that rises with the sea state. Controls: change drum speed (15 / 30 / 60 mm per minute: trace stretches); "change the paper" (the sheet lifts off, is initialled and dated in script, and files into a rack of previous days at the side; a fresh sheet wraps the drum); magnification ×1 / ×5 / ×25. Typography: observatory stationery: title in a modest engraved-style serif with small caps ("KETTLEWICK OBSERVATORY · SEISMOGRAPH No. 2 · VERTICAL COMPONENT"), handwritten-style italic annotations in ink (Georgia/Palatino italic, slightly rotated), typewriter face for telegram slips (Courier), tabular figures in the ledger. A short framed notice explains how to read P and S in three sentences. Entrance: the pen lowers onto the drum and immediately draws the tail end of an arriving earthquake so the first three seconds show a dramatic wavetrain decaying. Optional sound toggle (off by default): faint clockwork ticking and pen scratch whose loudness follows amplitude. Reduced motion: no page shudder; trace updates in one-second steps. DESCRIPTION A working observatory instrument presented as a page of stationery: an engraved masthead, a slate-and-brass elevation drawing of the seismograph (clockwork gearbox with a stepping escapement, a paper-wrapped drum sliding along its lead screw, long boom, knife-edge pivot, oil damper, sprung mass) and beneath it the unrolled recording sheet, where a simulated pen draws a continuous trace line by line. The page opens with the pen dropping onto the drum in the decaying surface waves of a distant earthquake, whose P, S and L flags, distance, magnitude nomogram, telegram and ledger entry appear as the first seconds pass. Everything the visitor does to the page (knocking, shaking, striking the pier with the mallet) is recorded by the same damped pen, annotated in red ink on the sheet and entered in the ledger with a dry remark. Analog readouts, a rack of filed sheets and a framed notice complete the bench. VISUAL TECHNIQUES - Canvas seismogram with cached completed lines, a live line, red time-marker lifts, phase flags with hairlines, rotated handwritten annotations and a procedural paper grain - Fixed-step simulation of a driven damped oscillator (pen) with stops that clip to a flat-topped trace - Deterministic signal model: band-limited microseisms with slow sea-state swells plus seeded teleseisms (P onset, S, dispersed surface waves, coda) scheduled from the real clock - Inline SVG elevation animated per frame: the drum's rings show the actual recent trace wrapped round the cylinder, the seam turns with the drum, the drum creeps along its lead screw, the boom, stylus, spring and damper vane move with the pen - Stepping brass escapement and gear train with spring-eased beats - SVG analog readouts: 24-hour dial, station-noise needle gauge, drum-speed needle, dwindling paper roll, ink vial - Three-scale magnitude nomogram whose geometry really solves M = log A + 2.76 log D − 2.48, with an animated red isopleth - Typewriter telegram slip with perforated edge; ledger with tabular figures and ink-in row reveals - Paper-change choreography: the sheet lifts, is dated and initialled in script, shrinks into the rack as a thumbnail, and a fresh sheet wraps in - Page shudder driven by its own damped spring; expanding red ring at each knock; custom mallet cursor - Optional synthesized sound: escapement ticks, pen scratch following pen velocity, pier thumps, telegraph key clicks INTERACTION MODEL Click, tap or thump anywhere on the page, or press Space: the page shudders slightly, the pen arm kicks and the trace records a spike that rings down; rapid knocks add up, and dragging quickly with the mouse held down (or physically shaking a phone) shakes the building, at high magnification driving the pen against its stops. "Strike the pier" delivers a calibrated mallet pulse. Each disturbance is annotated on the sheet and logged in the ledger a moment after it dies away. Segmented controls set drum speed (15 / 30 / 60 mm per minute, stretching the trace and rescaling the seconds rule) and magnification (×1 / ×5 / ×25). "Change the paper" lifts the sheet off, signs and dates it, files it in the rack and starts a fresh one with a full pen; this also happens by itself when the paper runs out. Scheduled distant earthquakes arrive every few minutes and trigger flags, the distance and magnitude reading, a typed telegram and a ledger entry. The sound toggle in the masthead is off by default. With reduced motion the shudder is removed and the trace and dials update once a second.