24 synoptic maps of 296 prominence average magnetic fields measured by Hanle effect during cycle XXI ascending phase

17 pages, 24 figures, submitted to Astronomy & Astrophysics, section "Catalogs and Data"Aims : The aim of the present paper is to publish 24 synoptic maps of solar filaments, in which 296 prominence average unambiguous magnetic field vectors were determined by Pic-du-Midi observations between 1974 and 1982, which is the ascending phase of cycle XXI. Methods : The magnetic field was determined by interpretation of the Hanle effect observed in the He I D3 line. Previous results about the prominence field polarity and prominence chirality were applied to solve the fundamental ambiguity. The measurements were averaged in each prominence for accuracy reasons. Results : The result is twofold. First, alternating field directions can be observed from one neutral line to the next one. Second, a general field alignment is found along a solar North-South field distorted under the differential rotation effect