Foucault's heliostat reflects the rays horizontally in any required direction.
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.
HELIOSTAT (from Gr.
Silbermann's heliostat reflects the rays in any direction.
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.