  Bernard Lyot invented the monochromatic birefringent filter in 1933 in order
to investigate the coronal emissions of solar structures above the limb with
the coronagraph installed at the Pic du Midi observatory. The filter was
improved later and he made the first observations of the chromosphere above the
solar disk in 1948, at Meudon. After his death, Grenat and Laborde continued
the development in the frame of the coming International Geophysical Year (IGY
1957-1958). A modern H$\alpha$ heliograph was completed soon and the flare
patrol started in 1956. This instrument was reproduced by two companies (SECASI
and OPL) and disseminated around the world in order to contribute to the IGY
common effort dedicated to the solar activity survey. We describe in this short
paper the capabilities of one of these copies operating at Haute Provence
station from 1958 to 1994.
