lituus
連鎖螺線
Lit·u·us n.; pl. Litui
1. Rom. Antig. (a) A curved staff used by the augurs in quartering the heavens. (b) An instrument of martial music; a kind of trumpet of a somewhat curved form and shrill note.
2. Math. A spiral whose polar equation is r²θ = a; that is, a curve the square of whose radius vector varies inversely as the angle which the radius vector makes with a given line.
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