The German physicist Hans Wolter was attempting to make an X-ray
microscope in the early 1950s. He applied the well-known fact that
X-rays can be reflected if they strike a smooth metal surface at a
grazing angle. He created 3 designs for systems which would focus, or
image, X-rays. He never made his microscope, however, because at the
time, mirrors could not be manufactured which were smooth enough.
Riccardo Giacconi, however, realized that the same designs could be
inverted and made as a telescope without such a stringent constraint on
the smoothness of the mirror.