Classical element to use the term "element (στοιχεῖον, "stoicheion")" in reference to air, fire, earth, and water. The ancient Greek word for element, "stoicheion" (from "stoicheo", "to line up") meant "smallest division (of a sun-dial), a syllable", as the composing unit of an alphabet it could denote a letter and the smallest unit from which a word is formed. A similar alphabetic metaphor may be the origin of the equivalent Latin word "elementum" (from which the English word comes), possibly based on the names of the letters 'l', 'm', and 'n', though the validity of this idea is debated. In his "On
Fusion ignition Fusion ignition Fusion ignition is the point at which a nuclear fusion reaction becomes self-sustaining. This occurs when the energy being given off by the fusion reactions heats the fuel mass more rapidly than various loss mechanisms cool it. At this point, the external energy needed to heat the fuel to fusion temperatures is no longer needed. As the rate of fusion varies with temperature, the point of ignition for any given machine is typically expressed as a temperature. Ignition should not be confused with "breakeven", a similar concept that compares the total energy being given off to the energy