<p>In magnetic observatories the Earth&#8217;s magnetic field is continuously recorded and the acquired data are calibrated so that the evolution of the field can be studied on time scales ranging from seconds to decades. The French network (the so called BCMT) includes 18 observatories around the world and the different types of data produced are freely accessible on several data centres. We will describe a typical infrastructure of a magnetic observatory, the measurement techniques, the instruments used, the general processing applied to obtain calibrated data and finally the environmental constraints that have to be respected in order to acquire suitable data. If magnetic observatories were originally set to monitor the slow variations of the Earth&#8217;s main magnetic field, they are more and more often used for space-weather monitoring and to study signal generated in the ionosphere and magnetosphere. This new range of applications implies an evolution of the network, of the acquisition and distribution techniques. The strategy we developed to respond to these new challenges will be also presented.</p>
VARIATIONS OF THE SOLAR ACTIVITY AND MAIN MAGNETIC FIELD OF THE EARTH IN THE SECOND MILLENNIUM C.E.
