A quartz thread thinner than a hair gave doctors the first readable heartbeat
Willem Einthoven's 1901 string galvanometer used a silvered quartz filament so light it visibly flickered when the heart's faint electrical currents passed through it. By 1903 he was recording clean, repeatable tracings of a beating human heart — the first practical electrocardiogram. He won the 1924 Nobel Prize in Physiology or Medicine for explaining what the ECG's waves actually meant.