贝尔的父亲甚至为聋人发明了一套所谓的“可见的语言”。 Bell's father had even gone so far as to develop a system of so-called "visible speech" for the deaf.
星座一览图天体球的一半或多半在平面图上的极投影图，这种图具有可调节的遮蔽物以显示在给定时刻和位置可见的恒星 A polar projection of half or more of the celestial sphere on a chart equipped with an adjustable overlay to show the stars visible at a particular time and place.
