One of the most important applications of the heliostat is as an adjunct to the newer forms of ' horizontal telescopes (q.v.) and in conjunction with spectroscopic telescopes in observations of eclipses.
In the absence of a heliostat it is more convenient to obtain a point of light with the aid of a lens of short focus.
In the absence of a heliostat the latter was the more convenient.
Silbermann's heliostat reflects the rays in any direction.
Foucault's heliostat reflects the rays horizontally in any required direction.