10 most difficult tech­nol­o­gy riddles

The origin of the logo may be traced back to a trip made by the 22-year-old André Citroën to Łódź city, Poland, where he discovered an innovative design for a chevron-shaped gear used in milling. He bought the patent for its application in steel and started his company which initially produced gears.

Cranberry glass or 'Gold Ruby' glass is a red glass made by adding gold salts or colloidal gold to molten glass. The glass is typically hand blown or molded. Legend holds that cranberry glass was first discovered when a noble tossed a gold coin into a mixture of molten glass

Argentina maintains the most permanent polar stations - 6, Chile - 5, Russia - 5.

The introduction of brown powder, which burned less rapidly than black powder, allowed to use longer barrels, which resulted in greater accuracy. Slower-burning powder decreases firing stresses, allowing guns to last longer and to be manufactured to tighter tolerances.

Some gas fittings use reverse threads to prevent disastrous misconnections. For example, oxygen fittings are right-handed, but acetylene and other flammable gases use left-handed fittings.

The Ku band is the portion of the electromagnetic spectrum in the microwave range of frequencies from 12 to 18 gigahertz (GHz). Ku band is primarily used for satellite communications, most notably for fixed and broadcast services, and for specific applications such as NASA's Tracking Data Relay Satellite used for both space shuttle and International Space Station

Iron is most abundant in the Earth's outer and inner core, and it is the fourth most common element in the Earth's crust.

1974 in Cadillac de Ville also saw the introduction of the optional "Air Cushion Restraint System". Known today as airbags, this option provided protection for front seat occupants in the case of a frontal collision. One bag was located in the steering wheel, the other in the dashboard in front of the front seat passenger.

On May 15, 1718, Englishman James Puckle patented his machine gun, the world's first! You may have thought the Gatling gun or the Maxim machine gun was the first machine gun, but depending on how you define “machine gun” James Puckle, Esq. (yes, he was a lawyer) got there first.

The green tint found in most tempered glass is a result of iron used in the production of glass sheets, where it is added as an ingredient to act as a lubricant. In fact, except in manufacturing processes designed to minimize iron use to avoid the green tint, you’ll find that green cast in all sheets of glass–not just tempered glass