Nabla W
Nabla may refer to any of the following: * the nabla symbol ∇ ** the vector differential operator, also called del, denoted by the nabla * Nabla, tradename of a type of rail fastening system (of roughly triangular shape) * ''Nabla'' (moth), a genus of moths * Nabla (instrument) The nevel or nebel ( he, נֵבֶל ''nēḇel'') was a stringed instrument used by the Israelites. The Greeks translated the name as ''nabla'' (νάβλα, "Phoenician harp"). A number of possibilities have been proposed for what kind of inst ...

Nabla Symbol
The nabla symbol The nabla is a triangular symbol resembling an inverted Greek delta:Indeed, it is called ( ανάδελτα) in Modern Greek. \nabla or ∇. The name comes, by reason of the symbol's shape, from the Hellenistic Greek word for a Phoenician harp, and was suggested by the encyclopedist William Robertson Smith to Peter Guthrie Tait in correspondence.Letter from Smith to Tait, 10 November 1870: My dear Sir, The name I propose for ∇ is, as you will remember, Nabla... In Greek the leading form is ναβλᾰ... As to the thing it is a sort of harp and is said by Hieronymus and other authorities to have had the figure of ∇ (an inverted Δ). Quoted in Oxford English Dictionary entry "nabla".Notably it is sometimes claimed to be from the Hebrew nevel (נֶבֶל)—as in the Book of Isaiah, 5th chapter, 12th sentence: "וְהָיָה כִנּוֹר וָנֶבֶל תֹּף וְחָלִיל וָיַיִן מִשְׁתֵּיהֶם וְאֵת פֹּעַל יְה� ...
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Rail Fastening System
A rail fastening system is a means of fixing rails to railroad ties (North America) or sleepers (British Isles, Australasia, and Africa). The terms ''rail anchors'', ''tie plates'', ''chairs'' and ''track fasteners'' are used to refer to parts or all of a rail fastening system. The components of a rail fastening system may also be known collectively as other track material, or OTM for short. Various types of fastening have been used over the years. History and overview The earliest wooden rails were fixed to wooden sleepers by pegs through holes in the rail, or by nails. By the 18th century, cast iron rails had come into use, and also had holes in the rail itself to allow them to be fixed to a support. 18th century developments such as the flanged rail and fish bellied rail also had holes in the rail itself; when stone block sleepers were used the nails were driven into a wooden block which had been inserted into a recess in the block. The first chair for a rail is thought to ...
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Nabla (moth)
''Nabla'' is a genus of moth in the family Geometridae The geometer moths are moths belonging to the family Geometridae of the insect order Lepidoptera, the moths and butterflies. Their scientific name derives from the Ancient Greek ''geo'' γεω (derivative form of or "the earth"), and ''met .... ReferencesNatural History Museum Lepidoptera genus database Geometridae Geometridae genera {{Geometridae-stub ...
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