sentences:  This instrument consists of a spectrograph combined with a polarimeter.The first instrument to be dedicated to the study of stellar magnetic fields was NARVAL, which was mounted on the Bernard Lyot Telescope at the Pic du Midi de Bigorre in the French Pyrenees mountains.Various measurements—including magnetometer measurements over the last 150 years; 14C in tree rings; and 10Be in ice cores—have established substantial magnetic variability of the Sun on decadal, centennial and millennial time scales.