A bronze bell was a precision tuned acoustic instrument, optimised over two thousand years of empirical craft. Two world wars melted hundreds of thousands of them for munitions.

Seventy eight percent copper, twenty two percent tin, unchanged since 1200 CE.

Bell metal is a tin bronze alloy in a tightly constrained range around 78 percent copper and 22 percent tin. The ratio was codified in Europe by 1200 CE and has not meaningfully changed since. Modern metallurgy explains why. Pure copper is too soft, damps vibration, and rings dull. Pure tin is too brittle and shatters. The 75 to 80 percent copper plus 25 to 20 percent tin window is the acoustic optimum: hard enough to ring, elastic enough to sustain, with a Young's modulus near 100 GPa and an internal damping Q factor above one thousand when properly cast. Outside the window the tonal quality collapses.

The convergence on the 78 to 22 ratio is craft empiricism arriving at a physical optimum without modern instrumentation. The same pattern of arrival appears in the rooftop ornament case the project's main thesis argues: a craft tradition converged on geometry that solves a physical problem, without necessarily framing the solution in our modern terms. Stradivari did not know elastic moduli. His violins still work. Medieval bell founders did not know Young's modulus. Their bells still ring.

A church bell rings five distinct tuned partials, deliberately shaped during casting.

A bell is not a single note. A properly tuned church bell sounds five harmonically related partial frequencies simultaneously. The bell founder tunes each one by shaving metal from specific annular zones inside the bell after casting, working entirely by ear, verified by striking tests, over weeks of iterative refinement. The five partials are universal across cathedral bell traditions in Europe and beyond.

The bell tierce is a minor third above the prime, not a major third, because the natural resonance of a bell shaped vibrator produces a minor third interval. European ear culture's acceptance of the minor third as consonant is a direct two thousand year exposure to bell overtones. Where a Pythagorean theorist would have predicted a major third from a string instrument's mathematical ratio, the bell delivered a minor third in every village every day, and the ear adapted. This is the cleanest example available of an entire continent's harmonic vocabulary being shaped by a single craft instrument.

A bell can carry beyond the five canonical partials. Superquint, decima major, decima minor, duodecima, and others appear in fully tuned cathedral bells. Seven harmonically related partials, in one bronze casting, audible kilometres from the tower.

The bourdon bell of a cathedral emits at 40 to 100 Hz. Some content reaches the infrasound band.

A large cathedral bourdon bell of one to three tons has a hum note in the 60 to 100 Hz range. The largest documented bells (the Petersglocke at Cologne Cathedral, the Pummerin at Vienna's Stephansdom, the great bell at Notre Dame, the Pakistani Maria Dolens) drop below 40 Hz at the fundamental. Below 20 Hz the sound becomes infrasonic to human hearing but remains a physical pressure wave. Infrasonic content propagates kilometres with minimal atmospheric attenuation, which is why bells were the audible time markers of pre modern village life across the entire continent.

Documented effects of infrasound at 15 to 25 Hz and over 80 dB include altered heart rate variability, sensation of awe and presence, occasional mild piloerection, and rare reports of vertigo. The relationship between bell infrasound and the documented physiological response of congregations and bystanders is a well established research area in environmental acoustics and psychoacoustics. The relationship between the systematic loss of bells in the two world wars and the modern urban acoustic environment is, by contrast, not measured.

Two world wars stripped the bells of central Europe for munitions, roughly 75 percent of the German inventory taken across two requisitions.

The losses are not in serious historical dispute. The Reichsglockenamt requisition records survive. The Vatican objected to the first round. Church and town histories carry the dates a particular town lost its peal. What is missing is the integrated cross national synthesis: a map of where bells survived, where they did not, and what the difference makes to the acoustic environment of those places now. That synthesis is the next research surface, and it is one of the experiments listed in the project's ten experiments index.

Three city pairs, twelve months, one infrasonic class one sound level meter.

Experiment seven in the ten experiments programme is the infrasound mapping proposal: deploy a Class 1 sound level meter with infrasonic capability at fixed radial points in three matched city pairs. Each pair has one city that retained its pre 1914 bell ringing tradition and one city that lost its bells to wartime requisition and never replaced them. Logged across a calendar year, the comparison tests whether the low frequency acoustic environment of the pre modern town centre is measurably different from its post war counterpart.

The connection to the rest of the antenna project: the same craft tradition that tuned bells tuned the proportions of the buildings beneath them. The same wartime requisitions stripped the bronze bells and stripped the ornamental iron. The same modernist aesthetic displaced both. The bell page is the acoustic companion to the rooftop ornament case. Its measurement, like the RF audit, is tractable, cheap, and unrun.