spherometer

[Gr. sphaira =a sphere, and Eng. meter.] An instrument for measuring the curvature of surfaces. It consists of a three-armed frame, standing on three steel pins, which form with each other an equilateral triangle; in the center of the instrument is a vertical screw with a fine thread, and having a large graduated head. sphër-o-si-dër-ite, 8. [SPHÆROSIDERITE.]