Edison's carbonized horsehair light bulb filament

Used to illustrate von Kármán's "engineer creates that which never was" — Edison created a working filament without understanding why horsehair worked. Lifespan ~11 hours.

So Brian Josephson did the calculation saying, electrons can go through insulating layers, and Bob Rose and Margaret did the experiment. Margaret graduated in two and a half years, went off as a Kennedy Fellow in England, came back here as an assistant professor of physics, and rose to Dean of Undergraduate Education, but died of brain cancer at about age 41 or 42. A scientist explains that which exists, and Brian Josephson made the mistake of solving the harder problem and not throwing out the insignificant term, which turned out not to be insignificant. On the other hand, engineers create things that never were, and they don't always know why they work. Edison — his first useful filament for a light bulb was what?