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silica
(Encyclopedia)silica or silicon dioxide, chemical compound, SiO2. It is insoluble in water, slightly soluble in alkalies, and soluble in dilute hydrofluoric acid. Pure silica is colorless to white. It occurs in sev...seeing
(Encyclopedia)seeing, in astronomy, the clarity with which stars and other celestial objects can be observed. It is primarily determined by the atmosphere of the earth. The most obvious phenomenon is twinkling, whe...tar and pitch
(Encyclopedia)tar and pitch, viscous, dark-brown to black substances obtained by the destructive distillation of coal, wood, petroleum, peat, and certain other organic materials. The heating or partial burning of w...latent heat
(Encyclopedia)latent heat, heat change associated with a change of state or phase (see states of matter). Latent heat, also called heat of transformation, is the heat given up or absorbed by a unit mass of a substa...europium
(Encyclopedia)europium yo͝orōˈpēəm [key] [from Europe], metallic chemical element; symbol Eu; at. no. 63; at. wt. 151.964; m.p. about 820℃; b.p. about 1,600℃; sp. gr. 5.25 at 25℃; valence +2 or +3. Europ...nursery
(Encyclopedia)nursery, in horticulture, an establishment or area for the propagation, breeding, and early cultivation of plants. In North America the term nursery originally specified a place where hardy woody plan...crossing over
(Encyclopedia)crossing over, process in genetics by which the two chromosomes of a homologous pair exchange equal segments with each other. Crossing over occurs in the first division of meiosis. At that stage each ...dengue fever
(Encyclopedia)dengue fever dĕngˈgē, –gā [key], acute infectious disease caused by four closely related viruses and transmitted by the bite of the female Aedes mosquito; it is also known as breakbone fever and...diagnosis
(Encyclopedia)diagnosis, determination of the nature of a disease or ailment. A clinical diagnosis is based on the medical history and physical examination of the patient: it may be confirmed with X-Rays, CAT Scans...Challenger expedition
(Encyclopedia)Challenger expedition, British oceanographic expedition under the direction of the Scottish professor Charles Wyville Thompson and the British naturalist Sir John Murray. Taking place from 1872 to 187...Browse by Subject
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