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"Cusp, in architecture, is the point formed by the meeting of two small arches, or foils, in foil arches, or tracery. Cusps often terminate in rich bosses of flowers and leaves." — Chambers' Encyclopedia, 1875

Cusp

"Cusp, in architecture, is the point formed by the meeting of two small arches, or foils, in foil arches,…

"Gold leaf electroscope; it consists of two strips of gold foil suspended from a brass rod within a glass jar. Used to detect the presence and sign of an electric charge." -Hawkins, 1917

Gold Leaf Electroscope

"Gold leaf electroscope; it consists of two strips of gold foil suspended from a brass rod within a…