Born in Aberdeen on this date, Nov. 6, in 1638, the Scottish mathematician, astronomer and inventor of the reflecting telescope, James Gregory. He was the first to investigate converging number series, which have an infinite number of terms but a finite sum. He made important contributions to the development of the calculus, although some of his best work remained virtually unknown until long after his death. In 1660 he published his Optica Promota, in which he described the first practical reflecting (Gregorian) telescope. Light reflected from a concave elliptical secondary mirror is brought to a focus just behind a hole in the primary mirror. It was superseded by the Newtonian and Cassegrain telescopes. Gregory also introduced estimation of stellar distances by photometric methods.