雙棱鏡; 雙棱柱體
Biprism \Bi"prism\, n. [Pref. bi- + prism.] 1. A prism whose refracting angle is very nearly 180 degrees. 2. A combination of two short rectangular glass prisms cemented together at their diagonal faces so as to form a cube; -- called also {optical cube}. It is used in one form of photometer.
biprism n : an optical device for obtaining interference fringes