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tachyon

(Encyclopedia)tachyon tăkˈēŏnˌ [key], hypothetical elementary particle that travels only at speeds exceeding that of light. According to the theory of relativity, the speed of light is the limiting velocity fo...

refraction

(Encyclopedia)refraction, in physics, deflection of a wave on passing obliquely from one transparent medium into a second medium in which its speed is different, as the passage of a light ray from air into glass. O...

Nakamura, Shuji

(Encyclopedia)Nakamura, Shuji, 1954–, Japanese physicist and electronics engineer, grad. Univ. of Tokushima (D.Eng., 1994). Nakamura joined the Nichia Corporation in 1977, and it was there that he began his life-...

Knights of Saint John of Jerusalem

(Encyclopedia)Knights of Saint John of Jerusalem: see Knights Hospitalers. ...

Saint John of Jerusalem, Knights of

(Encyclopedia)Saint John of Jerusalem, Knights of: see Knights Hospitalers. ...

mirror

(Encyclopedia)mirror, in optics, a reflecting surface that forms an image of an object when light rays coming from that object fall upon it (see reflection). Usually mirrors are made of plate glass, one side of whi...

promethium

(Encyclopedia)promethium prōmēˈthēəm [key], artificially produced radioactive chemical element; symbol Pm; at. no. 61; mass no. of most stable isotope 145; m.p. 1,042℃; b.p. 3,000℃ (estimated); sp. gr. unk...

fifth force

(Encyclopedia)fifth force, postulated fifth basic force of nature (the four known forces of nature are gravity, electromagnetism, and the strong and weak interactions). Proposed in 1986 to account for gravitational...

observatory

(Encyclopedia)observatory, scientific facility especially equipped to detect and record naturally occurring scientific phenomena. Although geological and meteorological observatories exist, the term is generally ap...

Stifter, Adalbert

(Encyclopedia)Stifter, Adalbert äˈdälbĕrt shtĭfˈtər [key], 1805–68, Austrian writer, b. Bohemia. Learned in law, mathematics, and science and accomplished as an artist, he was a tutor to important families...