The Scientist Who Invented the Thermos Refused to Patent It. Someone Else Made the Fortune.

US872795 and its related filings cover the vacuum flask as a commercial product. The person who invented the thing is not on any of them.

Sir James Dewar was a Scottish chemist and physicist at the Royal Institution in London, working at the frontier of low-temperature physics. In 1892 he needed a container that could hold liquefied gases — substances at hundreds of degrees below zero — long enough to study them. Everything he had leaked heat too fast.

His solution attacks all three modes of heat transfer at once, which is why it works so well.

Three problems, one object

Conduction is defeated by making the vessel double-walled and evacuating the gap between the walls. A vacuum has almost nothing in it to carry heat, so the inner vessel is nearly thermally disconnected from the outer one. The only remaining bridge is the narrow neck where the walls join.

Convection is defeated by the same vacuum: no air means no circulating currents.

Radiation is defeated by silvering both facing surfaces of the gap, so infrared energy is reflected back where it came from rather than absorbed.

The result holds hot things hot and cold things cold with equal indifference, which is the source of the old joke about how it knows.

The gift

Dewar published the design and refused to patent it.

His position, consistent with the culture of the Royal Institution and with his own view of himself as a scientist rather than a manufacturer, was that a laboratory instrument belonged to science. He wanted other researchers to build them freely.

He appears never to have considered that anyone outside a laboratory would want one.

Thermos

Dewar contracted the delicate glassblowing to outside craftsmen. Among them was Reinhold Burger, a German glassblower, who did see the consumer application: a flask that keeps coffee hot is useful to anyone who eats lunch away from home.

Burger encased the fragile glass vessel in a protective metal housing — the practical change that turned a laboratory apparatus into something a person could carry in a lunchbox — patented the commercial article in Germany in 1903, and ran a public competition to name it. The winning entry was Thermos, from the Greek for heat.

The product was an immediate international success. Thermos flasks went with Peary toward the North Pole, with Shackleton to the Antarctic, and up in early aircraft and balloons, and the publicity from those expeditions built the brand.

Dewar sued, and lost. He had published the design openly; there was nothing left to claim.

He remained an eminent scientist, was knighted, and never earned anything from the vacuum flask. Thermos became so dominant that in the United States the trademark was eventually ruled generic — the word had become the ordinary English name for the object, which is the last thing that happens to a brand before it disappears into the language.

See the original

The full text and figures of US872795 are on patents.us.