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allotropy

(Encyclopedia)allotropy əlŏˈtrəpē [key] [Gr.,=other form]. A chemical element is said to exhibit allotropy when it occurs in two or more forms in the same physical state; the forms are called allotropes. Allot...

Biosphere 2

(Encyclopedia)Biosphere 2, privately funded ecological research project in which eight people lived sealed in a 3.15-acre (1.28-hectare) structure for two years (Sept. 26, 1991–Sept. 26, 1993). Located in Oracle,...

gram-atomic weight

(Encyclopedia)gram-atomic weight, amount of an atomic substance whose weight, in grams, is numerically equal to the atomic weight of that substance. For example, 1 gram-atomic weight of atomic oxygen, O (atomic wei...

photosynthesis

(Encyclopedia)photosynthesis fōˌtōsĭnˈthəsĭs [key], process in which green plants, algae, and cyanobacteria utilize the energy of sunlight to manufacture carbohydrates from carbon dioxide and water in the pr...

stress test

(Encyclopedia)stress test or exercise electrocardiography, in medicine, a test that evaluates the performance of the heart by subjecting it to controlled amounts of physical stress. Such tests, which include walkin...

stromatolite

(Encyclopedia)stromatolite, layered structures produced by the binding together of sediments by a thin layer of cyanobacteria. The layers, which are deposited very slowly, gradually produce rounded or hummocklike f...

eutrophication

(Encyclopedia)eutrophication yo͞otrōˌfĭkāˈshən [key], aging of a lake by biological enrichment of its water. In a young lake the water is cold and clear, supporting little life. With time, streams draining i...

blast furnace

(Encyclopedia)CE5 Blast furnace for production of iron blast furnace, structure used chiefly in smelting. The principle involved in this means of extracting metals is that of the reduction of the ores by the ac...

cinnabar

(Encyclopedia)cinnabar sĭnˈəbär [key], mineral, the sulfide of mercury, HgS. Deep red in color, it is used as a pigment (see vermilion), but principally it is a source of the metal mercury. It is mined in Spain...

Menzel, Donald Howard

(Encyclopedia)Menzel, Donald Howard, 1901–76, American astrophysicist, b. Florence, Colo. From 1926 to 1932 he was with the Lick Observatory in Calif. In 1932 he joined the faculty at Harvard, where he became pro...