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Dollond, John

(Encyclopedia)Dollond, John dŏlˈənd [key], 1706–61, English optician and inventor. A silk weaver, he taught himself languages, mathematics, and science, becoming a noted scholar as well as a scientist. He inve...

relay

(Encyclopedia)relay, electromechanical switch operated by a flow of electricity in one circuit and controlling the flow of electricity in another circuit. A relay consists basically of an electromagnet with a soft ...

Airy, Sir George Biddell

(Encyclopedia)Airy, Sir George Biddell, 1801–92, English astronomer. The son of a poor farmer, he distinguished himself as Senior Wrangler at Cambridge, where he was elected fellow of Trinity College (1824) and a...

rheostat

(Encyclopedia)rheostat rēˈəstătˌ [key], device whose resistance to electric current depends on the position of some mechanical element or control in the device. Typically a rheostat consists of a resistance el...

galactosemia

(Encyclopedia)galactosemia gəlăkˌtəsēˈmēə [key], inherited metabolic disorder caused by an enzyme deficiency and transmitted as a recessive trait; it results in the accumulation of the sugar galactose in th...

telescope

(Encyclopedia)CE5 Mirror arrangements for a reflecting telescope telescope, traditionally, a system of lenses, mirrors, or both, used to gather light from a distant object and form an image of it. Traditional o...

touch

(Encyclopedia)touch, tactile sensation received by the skin, enabling the organism to detect objects or substances in contact with the body. End organs (nerve endings) in the skin convey the impression to the brain...

chloroplast

(Encyclopedia)chloroplast klōrˈəplăstˌ, klôrˈ– [key], a complex, discrete green structure, or organelle, contained in the cytoplasm of plant cells. Chloroplasts are reponsible for the green color of almost...

yaws

(Encyclopedia)yaws or frambesia, tropical infection of the skin caused by a spirochete (Treponema pertenue) closely related to that causing syphilis. Yaws, however, is not a sexually transmitted disease, i.e., it i...

Fracastoro, Girolamo

(Encyclopedia)Fracastoro, Girolamo jērôˈlämō fräkästôˈrō [key], 1483–1553, Italian physician and poet. He was born in Verona, where he practiced after studying at Padua. He studied epidemic diseases and...