RAAB, H. English: Double Refractor at the Fabra Observatory, Barcelona. The visual instrument (the lower of the two tubes) has an aperture of 38 cm and a focal length of 6 meters (f/15.8). The photographic instrument also has an aperture of 38 cm, but a shorter focal length of 4 meters (f/10.5). The Instrument was built by Mailhat, Paris, in 1904.. [s.l.]: [s.n.] Dostupné online.
