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glass

(Encyclopedia)glass, hard substance, usually brittle and transparent, composed chiefly of silicates and an alkali fused at high temperature. Glass has become invaluable in modern architecture, illumination, elect...

quantum theory

(Encyclopedia)quantum theory, modern physical theory concerned with the emission and absorption of energy by matter and with the motion of material particles; the quantum theory and the theory of relativity togethe...

atom

(Encyclopedia)CE5 Bohr-Rutherford atom CE5 Probability distribution of the electron in the hydrogen atom: A. Ground state B. Highly excited state atom [Gr.,=uncuttable (indivisible)], basic unit of matte...

niobium

(Encyclopedia)niobium nīōˈbēəm [key], metallic chemical element; symbol Nb; at. no. 41; at. wt. 92.90638; m.p. about 2,468℃; b.p. 4,742℃; sp. gr. 8.57 at 20℃; valence +2, +3, +4, or +5. Niobium is a rare...

Astor, John Jacob, 1763–1848, American merchant

(Encyclopedia)Astor, John Jacob ăsˈtər [key], 1763–1848, American merchant, b. Walldorf, near Heidelberg, Germany. At the age of 16 he went to England, and five years later, in 1784, he arrived in Baltimore, p...

mixture

(Encyclopedia)mixture, in chemistry, a physical combination of two or more pure substances (i.e., elements or compounds). A mixture is distinguished from a compound, which is formed by the chemical combination of t...

sage

(Encyclopedia)sage, any species of the large genus Salvia, aromatic herbs or shrubs of the family Labiatae (mint family). The common sage of herb gardens is S. officinalis, a strongly scented shrubby perennial, nat...

scandium

(Encyclopedia)scandium skănˈdēəm [key], metallic chemical element; symbol Sc; at. no. 21; at. wt. 44.95591; m.p. 1,541℃; b.p. 2,831℃; sp. gr. 2.99 at 20℃; valence +3. Scandium is a soft silver-white metal...

combinatorics

(Encyclopedia)combinatorics kŏmˌbĭnətôrˈēəl [key], sometimes called the science of counting, the branch of mathematics concerned with the selection, arrangement, and operation of elements within sets. Combi...

contour

(Encyclopedia)contour or contour line, line on a topographic map connecting points of equal elevation above or below mean sea level. It is thus a kind of isopleth, or line of equal quantity. Contour lines are drawn...