Spinning Mirrors of Mercury

Abstract

pool of pure, silver-white mercury A makes a flawless, natural mirror. Spin the pool, and centrifugal force shapes its flat surface into a parabola. Attach this concave to the proper electronic equipment, aim it into the sky on a cloudless night, and it becomes a powerful optical telescope. This is the theory behind the mirror telescopes that astrophysicist Ermanno F Borra has built at Universite Laval in Quebec, Canada. He has made three prototypes-two of them 1 meter in diameter and the third 1.65 meters and he is using a 1-meter model this summer to look for rapid variations in the sky. Although the concept of using spinning mercury as a telescope reflector is at least two centuries old and has been attempted many times since at least 1909, Borra claims he is the first to make it work. He says he has learned to control precisely the speed of the mirror's rotation, to keep wind-generated waves from the surface of the mercury and to keep the poisonous mercury from harming telescope operators. Laboratory tests done in 1984 and 1985 demonstrated that his parabola of spinning mercury maintains a constant shape and a stable focus, Borra says. already have proved that the concept is sound, he told SCIENCE NEWS. The only thing I have to prove now is that I can make very large liquid mirrors.